Multivitamin

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Multivitamins contain multiple micro-nutrients, such as vitamins and dietary minerals. B vitamin supplement tablets.jpg
Multivitamins contain multiple micro-nutrients, such as vitamins and dietary minerals.

A multivitamin is a preparation intended to serve as a dietary supplement with vitamins, dietary minerals, and other nutritional elements. Such preparations are available in the form of tablets, capsules, pastilles, powders, liquids, gummies, or injectable formulations. Other than injectable formulations, which are only available and administered under medical supervision, multivitamins are recognized by the Codex Alimentarius Commission (the United Nations' authority on food standards) as a category of food. [1]

Contents

In healthy people, most scientific evidence indicates that multivitamin supplements do not prevent cancer, heart disease, or other ailments, and regular supplementation is not necessary. [2] [3] [4] [5] [6] [7] [8] However, specific groups of people may benefit from multivitamin supplements, for example, people with poor nutrition or those at high risk of macular degeneration, [3] [9] and women who are pregnant or trying to get pregnant. [10]

There is no standardized scientific definition for multivitamin. [11] In the United States, a multivitamin/mineral supplement is defined as a supplement containing three or more vitamins and minerals that does not include herbs, hormones, or drugs, where each vitamin and mineral is included at a dose below the tolerable upper intake level as determined by the Food and Drug Board, and does not present a risk of adverse health effects. [12]

Products and components

Many multivitamin formulas contain vitamin C, B1, B2, B3, B5, B6, B7, B9, B12, A, E, D2 (or D3), K, potassium, iodine, selenium, borate, zinc, calcium, magnesium, manganese, molybdenum, beta carotene, and/or iron. Multivitamins are typically available in a variety of formulas based on age and sex, or (as in prenatal vitamins) based on more specific nutritional needs; a multivitamin for men might include less iron, while a multivitamin for seniors might include extra vitamin D. Some formulas make a point of including extra antioxidants.

Some nutrients, such as calcium and magnesium, are rarely included at 100% of the recommended allowance because the pill would become too large in size. Most multivitamins come in capsule form; tablets, powders, liquids, and injectable formulations also exist. In the United States, the FDA requires any product marketed as a "multivitamin" to contain at least three vitamins and minerals; furthermore, the dosages must be below a "tolerable upper limit", and a multivitamin may not include herbs, hormones, or drugs. [13]

Uses

For certain people, particularly for older people, supplementing the diet with additional vitamins and minerals can have health impacts; however, the majority will not benefit. [14] People with dietary imbalances may include those on restrictive diets and those who cannot or will not eat a nutritious diet. Pregnant women and elderly adults have different nutritional needs compared to other adults, and a multivitamin may be indicated by a physician. Generally, medical advice is to avoid multivitamins during pregnancy, particularly those containing vitamin A, unless they are recommended by a health care professional. However, the NHS recommends 10μg of Vitamin D per day throughout the pregnancy and while breastfeeding, and 400μg of folic acid during the first trimester (first 12 weeks of pregnancy). [15] Some women may need to take iron, vitamin C, or calcium supplements during pregnancy, but only on the advice of a doctor.

In the 1999–2000 National Health and Nutrition Examination Survey, 52% of adults in the United States reported taking at least one dietary supplement in the last month and 35% reported regular use of multivitamin-multimineral supplements. Women versus men, older adults versus younger adults, non-Hispanic whites versus non-Hispanic blacks, and those with higher education levels versus lower education levels (among other categories) were more likely to take multivitamins. Individuals who use dietary supplements (including multivitamins) generally report higher dietary nutrient intakes and healthier diets. Additionally, adults with a history of prostate and breast cancers were more likely to use dietary and multivitamin supplements. [16]

Precautions

Bell curve of intake versus health effect.svg

The amounts of each vitamin type in multivitamin formulations are generally adapted to correlate with what is believed to result in optimal health effects in large population groups. However, these standard amounts may not correlate with what is optimal in certain subpopulations, such as in children, pregnant women and people with certain medical conditions and medication.

The health benefit of vitamins generally follows a biphasic dose-response curve, taking the shape of a bell curve, with the area in the middle being the safe-intake range and the edges representing deficiency and toxicity. [17] For example, the Food and Drug Administration recommends that adults on a 2,000 calorie diet get between 60 and 90 milligrams of vitamin C per day. [18] This is the middle of the bell curve. The upper limit is 2,000 milligrams per day for adults, which is considered potentially dangerous. [19]

In particular, pregnant women should consult their doctors before taking any multivitamins. For example, either an excess or deficiency of vitamin A can cause birth defects. [20]

Long-term use of beta-carotene, vitamin A, and vitamin E supplements may shorten life, [2] and increase the risk of lung cancer in people who smoke (especially those smoking more than 20 cigarettes per day), former smokers, people exposed to asbestos, and those who use alcohol. [21] Many common brand supplements in the United States contain levels above the DRI/RDA amounts for some vitamins or minerals.

Severe vitamin and mineral deficiencies require medical treatment and can be very difficult to treat with common over-the-counter multivitamins. In such situations, special vitamin or mineral forms with much higher potencies are available, either as individual components or as specialized formulations.

Multivitamins in large quantities may pose a risk of an acute overdose due to the toxicity of some components, principally iron. However, in contrast to iron tablets, which can be lethal to children, [22] toxicity from overdoses of multivitamins are very rare. [23] There appears to be little risk to supplement users of experiencing acute side effects due to excessive intakes of micronutrients. [24] There also are strict limits on the retinol content for vitamin A during pregnancies that are specifically addressed by prenatal formulas.

As noted in dietary guidelines from Harvard School of Public Health in 2008, multivitamins should not replace healthy eating or make up for unhealthy eating. [25] [ failed verification ] In 2015, the U.S. Preventive Services Task Force analyzed studies that included data for about 450,000 people. The analysis found no clear evidence that multivitamins prevent cancer or heart disease, helped people live longer, or "made them healthier in any way." [26]

Research

Provided that precautions are taken (such as adjusting the vitamin amounts to what is believed to be appropriate for children, pregnant women or people with certain medical conditions), multivitamin intake is generally safe, but research is still ongoing with regard to what health effects multivitamins have.

Evidence of health effects of multivitamins comes largely from prospective cohort studies, which evaluate health differences between groups that take multivitamins and groups that do not. Correlations between multivitamin intake and health found by such studies may not result from multivitamins themselves, but may reflect underlying characteristics of multivitamin-takers. For example, it has been suggested that multivitamin-takers may, overall, have more underlying diseases (making multivitamins appear as less beneficial in prospective cohort studies). [27] On the other hand, it has also been suggested that multivitamin users may, overall, be more health-conscious (making multivitamins appear as more beneficial in prospective cohort studies). [28] [29] Randomized controlled studies have been encouraged to address this uncertainty. [30]

Cohort studies

Centrum multivitamins produced by Pfizer, which were used in Physicians' Health Study II Wyeth Centrum.jpg
Centrum multivitamins produced by Pfizer, which were used in Physicians' Health Study II

In February 2009, a study conducted in 161,808 postmenopausal women from the Women's Health Initiative clinical trials concluded that after eight years of follow-up "multivitamin use has little or no influence on the risk of common cancers, cardiovascular disease, or total mortality". [29] Another 2010 study in the Journal of Clinical Oncology suggested that multivitamin use during chemotherapy for stage III colon cancer had no effect on the outcomes of treatment. [31] A very large prospective cohort study published in 2011, including more than 180,000 participants, found no significant association between multivitamin use and mortality from all causes. The study also found no impact of multivitamin use on the risk of cardiovascular disease or cancer. [32]

A cohort study that received widespread media attention [33] [34] is the Physicians' Health Study II (PHS-II). [35] PHS-II was a double-blind study of 14,641 male U.S. physicians initially aged 50 years or older (mean age of 64.3) that ran from 1997 to June 1, 2011. The mean time that the men were followed was 11 years. The study compared total cancer (excluding non-melanoma skin cancer) for participants taking a daily multivitamin (Centrum Silver by Pfizer) versus a placebo. Compared with the placebo, men taking a daily multivitamin had a small but statistically significant reduction in their total incidence of cancer. In absolute terms, the difference was just 1.3 cancer diagnoses per 1000 years of life. The hazard ratio for cancer diagnosis was 0.92 with a 95% confidence interval spanning 0.86–0.998 (P = .04); this implies a benefit of between 14% and .2% over placebo in the confidence interval. No statistically significant effects were found for any specific cancers or for cancer mortality. As pointed out in an editorial in the same issue of the Journal of the American Medical Association , the investigators observed no difference in the effect whether the study participants were or were not adherent to the multivitamin intervention, which diminishes the dose–response relationship. [36] The same editorial argued that the study did not properly address the multiple comparisons problem, in that the authors neglected to fully analyze all 28 possible associations in the study—they argue if this had been done, the statistical significance of the results would be lost. [36]

Using the same PHS-II study, researchers concluded that taking a daily multivitamin did not have any effect in reducing heart attacks and other major cardiovascular events, MI, stroke, and CVD mortality. [37]

Systematic reviews and meta-analyses

One major meta-analysis published in 2011, including previous cohort and case-control studies, concluded that multivitamin use was not significantly associated with the risk of breast cancer. It noted that one Swedish cohort study has indicated such an effect, but with all studies taken together, the association was not statistically significant. [30] A 2012 meta-analysis of ten randomized, placebo-controlled trials published in the Journal of Alzheimer's Disease found that a daily multivitamin may improve immediate recall memory, but did not affect any other measure of cognitive function. [38]

Another meta-analysis, published in 2013, found that multivitamin-multimineral treatment "has no effect on mortality risk", [39] and a 2013 systematic review found that multivitamin supplementation did not increase mortality and might slightly decrease it. [40] A 2014 meta-analysis reported that there was "sufficient evidence to support the role of dietary multivitamin/mineral supplements for the decreasing the risk of age-related cataracts." [41] A 2015 meta-analysis argued that the positive result regarding the effect of vitamins on cancer incidence found in Physicians' Health Study II (discussed above) should not be overlooked despite the neutral results found in other studies.

Looking at 2012 data, a study published in 2018 presented meta-analyses on cardiovascular disease outcomes and all-cause mortality. It found that "conclusive evidence for the benefit of any supplement across all dietary backgrounds (including deficiency and sufficiency) was not demonstrated; therefore, any benefits seen must be balanced against possible risks." The study dismissed the benefits of routinely taking supplements of vitamins C and D, beta-carotene, calcium, and selenium. Results indicated taking niacin may actually be harmful. [4] [5]

In July 2019, another meta-analysis of 24 interventions in 277 trials was conducted and published in Annals of Internal Medicine , including a total of almost 1,000,000 participants. [7] The study generally concluded that the vast majority of multivitamins had no significant effect on survival or heart attack risk. [42] The study found a significant effect on heart health in a low-salt diet, and a small effect due to omega-3 and folic acid supplements. [43] This analysis supports the results of two early 2018 studies that found no conclusive benefits from multivitamins for healthy adults. [6] [44]

Expert bodies

A 2006 report by the U.S. Agency for Healthcare Research and Quality concluded that "regular supplementation with a single nutrient or a mixture of nutrients for years has no significant benefits in the primary prevention of cancer, cardiovascular disease, cataract, age-related macular degeneration or cognitive decline." [9] However, the report noted that multivitamins have beneficial effects for certain sub-populations, such as people with poor nutritional status, that vitamin D and calcium can help prevent fractures in older people, and that zinc and antioxidants can help prevent age-related macular degeneration in high-risk individuals. [9] A 2017 Cochrane Systematic Review found that multivitamins including vitamin E or beta carotene will not delay the onset of macular degeneration or prevent the disease, [45] however, some people with macular degeneration may benefit from multivitamin supplementation as there is evidence that it may delay the progression of the disease. [46] [ needs update ] Including lutein and zeaxanthin supplements in with a multivitamin does not improve progression of macular degeneration. [46] The need for high-quality studies looking at the safety of taking multivitamins has been highlighted. [46]

According to the Harvard School of Public Health: "... many people don't eat the healthiest of diets. That's why a multivitamin can help fill in the gaps, and may have added health benefits." [47] The U.S. Office of Dietary Supplements, a branch of the National Institutes of Health, suggests that multivitamin supplements might be helpful for some people with specific health problems (for example, macular degeneration). However, the Office concluded that "most research shows that healthy people who take an MVM [multivitamin] do not have a lower chance of diseases, such as cancer, heart disease, or diabetes. Based on current research, it's not possible to recommend for or against the use of MVMs to stay healthier longer." [3]

Life expectancy

A 2024 study of 390,124 healthy adults found that use of multivitamins did not extend life expectancy. [48]

History and debate

The history of multivitamins begins in the early 20th century when advancements in nutritional science led to the discovery of essential vitamins and minerals. Initially, multivitamins were designed to respond to widespread nutritional deficiencies. [49] These supplements were seen as a practical solution to combat malnutrition, improving public health by providing vital nutrients that were otherwise scarce.

As the 20th century progressed, the use of multivitamins expanded beyond addressing deficiencies. With the rise of the wellness industry, [50] they became popularized as a convenient way to enhance overall health, even for those with access to sufficient nutrition. However, as marketing strategies evolved, the emphasis shifted from necessity to preventative health and general well-being, [51] often without sound scientific backing.

The role of multivitamins has since been increasingly questioned. Some still view them as beneficial, especially in cases of specific deficiencies. A growing body of research suggests that for many people, multivitamins act more as a placebo than a necessary supplement. This indicates a shift in the epistemology of vitamins, where people are generally more aware of them and their properties but there is a gap in their knowledge of the scientific research surrounding them

Studies have shown that multivitamins can have positive effects on mood and energy, [52] [53] but there is little evidence to support an increase in general health and life expectancy. [54] [55]  

Under the Dietary Supplement Health and Education Act (DSHEA), passed in 1994 in the United States, the Food and Drug Administration (FDA) is not responsible for testing the risks and efficacy of dietary supplements. Manufacturers are not required to present data on the effectiveness of multivitamins or disclose known side effects to the FDA. Furthermore, manufacturers are not required to test human safety of dietary supplements. [56]

Ethnographic research

Ethnographic research has investigated possible reasons behind the widespread use of multivitamins in societies where scientific knowledge is dominant, despite the limited empirical evidence supporting new products. [57] [50] The findings reveal various socio-cultural factors contributing to their common use, including:

From anthropological and psychological perspectives, the widespread consumption of multivitamins can be seen as an example of 'magical thinking,' a form of reasoning that seeks to explain phenomena through non-scientific means, distinct from 'irrational thinking’. [57] [58]

ASD Research

In 2019, a systematic review and meta-analysis examining the relationship between ‘maternal multivitamin supplementation’ and children being diagnosed with autism spectrum disorder (ASD) was published in Nutritional Research. The research was conducted in the previous year and involved using the ‘random effects’ model on 9 independent trials consisting of 231,163 children across 4459 cases. The results of this study indicated that pregnant women using multivitamin supplements during the prenatal period reduced the risk of their children being diagnosed with autism compared to their counterparts. Furthermore, the systematic review and meta-analysis found that women who took multivitamins prior to becoming pregnant saw a further reduced risk. The authors recommend further study. [59]

In 2021, a similar systematic review and meta-analysis examining the relationship between prenatal multivitamins and children being diagnosed with autism spectrum disorder (ASD) was published in Nutrients. The study involved 904,947 children encompassing 8159 cases. The study concluded that while no distinct association was found, there was substantial evidence of reduced risk in high quality studies, multivitamin use during early pregnancy, tested prospective studies and evidence following the removal of a single outlier study. [60]

Regulations

United States

The first person to formulate vitamins in the US was Dr. Forrest C. Shaklee. [61] Shaklee introduced a product he dubbed "Shaklee's Vitalized Minerals" in 1915, which he sold until adopting the now ubiquitous term "vitamin" in 1929. [62]

Because of their categorization as a dietary supplement by the Food and Drug Administration (FDA), most multivitamins sold in the U.S. are not required to undergo the testing procedures typical of pharmaceutical drugs. However, some multivitamins contain very high doses of one or several vitamins or minerals, or are specifically intended to treat, cure, or prevent disease, and therefore require a prescription or medicinal license in the U.S. Since such drugs contain no new substances, they do not require the same testing as would be required by a New Drug Application, but were allowed on the market as drugs due to the Drug Efficacy Study Implementation program. [63]

Australia

Vitamins are classed as low-risk medications by the Therapeutic Goods Administration (TGA), and are therefore not assessed for efficacy, unlike most medicines sold in Australia. They require that the product is safe and that claims of efficacy can only be made in regards to minor ailments. No claims can be made about serious conditions. The TGA does not examine the contents of the product and whether it is what the label says it is, but they claim to carry out "targeted and random surveillance of products on the market." [64] They encourage people to report any unsafe products to them.

The TGA, however, has been criticized, by people such as Allan Asher, a regulatory expert and former deputy chair of the Australian Competition & Consumer Commission, for allowing more than a thousand types of claim, 86% of which are not supported by scientific evidence, including "softens hardness", "replenishes gate of vitality" and "moistens dryness in the triple burner". [65]

See also

Related Research Articles

Omega−3 fatty acids, also called omega−3 oils, ω−3 fatty acids or n−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond three atoms away from the terminal methyl group in their chemical structure. They are widely distributed in nature, being important constituents of animal lipid metabolism, and they play an important role in the human diet and in human physiology. The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA can be found in plants, while DHA and EPA are found in algae and fish. Marine algae and phytoplankton are primary sources of omega−3 fatty acids. DHA and EPA accumulate in fish that eat these algae. Common sources of plant oils containing ALA include walnuts, edible seeds, and flaxseeds as well as hempseed oil, while sources of EPA and DHA include fish and fish oils, and algae oil.

<span class="mw-page-title-main">Vitamin C</span> Essential nutrient found in citrus fruits and other foods

Vitamin C is a water-soluble vitamin found in citrus and other fruits, berries and vegetables. It is also a generic prescription medication and in some countries is sold as a non-prescription dietary supplement. As a therapy, it is used to prevent and treat scurvy, a disease caused by vitamin C deficiency.

The term Vitamin E refers to a group of eight molecular-structure related compounds that include four tocopherols and four tocotrienols. The tocopherols function as fat-soluble antioxidants which may help protect cell membranes from reactive oxygen species. Vitamin E is classified as an essential nutrient for humans. Various government organizations recommend that adults consume between 3 and 15 mg per day, while a 2016 worldwide review reported a median dietary intake of 6.2 mg per day. Sources rich in vitamin E include seeds, nuts, seed oils, peanut butter, vitamin E-fortified foods, and dietary supplements. Symptomatic vitamin E deficiency is rare, is usually caused by an underlying problem with digesting dietary fat rather than from a diet low in vitamin E. Deficiency can cause neurological disorders.

Tocopherols are a class of organic compounds comprising various methylated phenols, many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, it was named tocopherol, from Greek τόκοςtókos 'birth' and φέρεινphérein 'to bear or carry', that is 'to carry a pregnancy', with the ending -ol signifying its status as a chemical alcohol.

<span class="mw-page-title-main">Folate</span> Vitamin B9; nutrient essential for DNA synthesis

Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and storage. Folate is required for the body to make DNA and RNA and metabolise amino acids necessary for cell division and maturation of blood cells. As the human body cannot make folate, it is required in the diet, making it an essential nutrient. It occurs naturally in many foods. The recommended adult daily intake of folate in the U.S. is 400 micrograms from foods or dietary supplements.

<span class="mw-page-title-main">Dietary supplement</span> Product providing additional nutrients

A dietary supplement is a manufactured product intended to supplement a person's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources, or that are synthetic. The classes of nutrient compounds in supplements include vitamins, minerals, fiber, fatty acids, and amino acids. Dietary supplements can also contain substances that have not been confirmed as being essential to life, and so are not nutrients per se, but are marketed as having a beneficial biological effect, such as plant pigments or polyphenols. Animals can also be a source of supplement ingredients, such as collagen from chickens or fish for example. These are also sold individually and in combination, and may be combined with nutrient ingredients. The European Commission has also established harmonized rules to help insure that food supplements are safe and appropriately labeled.

Orthomolecular medicine is a form of alternative medicine that claims to maintain human health through nutritional supplementation. It is rejected by evidence-based medicine. The concept builds on the idea of an optimal nutritional environment in the body and suggests that diseases reflect deficiencies in this environment. Treatment for disease, according to this view, involves attempts to correct "imbalances or deficiencies based on individual biochemistry" by use of substances such as vitamins, minerals, amino acids, trace elements and fatty acids. The notions behind orthomolecular medicine are not supported by sound medical evidence, and the therapy is not effective for chronic disease prevention; even the validity of calling the orthomolecular approach a form of medicine has been questioned since the 1970s.

<span class="mw-page-title-main">Mediterranean diet</span> Diet inspired by the Mediterranean region

The Mediterranean diet is a concept first invented in 1975 by the American biologist Ancel Keys and chemist Margaret Keys. The diet took inspiration from the eating habits and traditional food typical of Crete, much of the rest of Greece, and southern Italy, and formulated in the early 1960s. It is distinct from Mediterranean cuisine, which covers the actual cuisines of the Mediterranean countries, and from the Atlantic diet of northwestern Spain and Portugal. While inspired by a specific time and place, the "Mediterranean diet" was later refined based on the results of multiple scientific studies.

<span class="mw-page-title-main">Cardiovascular disease</span> Class of diseases that involve the heart or blood vessels

Cardiovascular disease (CVD) is any disease involving the heart or blood vessels. CVDs constitute a class of diseases that includes: coronary artery diseases, heart failure, hypertensive heart disease, rheumatic heart disease, cardiomyopathy, arrhythmia, congenital heart disease, valvular heart disease, carditis, aortic aneurysms, peripheral artery disease, thromboembolic disease, and venous thrombosis.

β-Carotene Red-orange pigment of the terpenoids class

β-Carotene (beta-carotene) is an organic, strongly colored red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 carbons.

<span class="mw-page-title-main">Plant-based diet</span> Diet consisting mostly or entirely of plant-based foods

A plant-based diet is a diet consisting mostly or entirely of plant-based foods. It encompasses a wide range of dietary patterns that contain low amounts of animal products and high amounts of fiber-rich plant products such as vegetables, fruits, whole grains, legumes, nuts, seeds, herbs, and spices. Plant-based diets may also be vegan or vegetarian but do not have to be, as they are defined in terms of high frequency of plants and low frequency of animal food consumption.

<span class="mw-page-title-main">Vegetarian nutrition</span> Nutritional and human health aspects of vegetarian diets

Vegetarian nutrition is the set of health-related challenges and advantages of vegetarian diets.

The Age-Related Eye Disease Study (AREDS) was a clinical trial sponsored by the National Eye Institute that ran from 1992 to 2001. The study was designed to:

<span class="mw-page-title-main">Women's Health Initiative</span> Long-term U.S. health study

The Women's Health Initiative (WHI) was a series of clinical studies initiated by the U.S. National Institutes of Health (NIH) in 1991, to address major health issues causing morbidity and mortality in postmenopausal women. It consisted of three clinical trials (CT) and an observational study (OS). In particular, randomized controlled trials were designed and funded that addressed cardiovascular disease, cancer, and osteoporosis.

<span class="mw-page-title-main">Red meat</span> Meat which is red when raw, with high myoglobin content

In gastronomy, red meat is commonly red when raw, in contrast to white meat, which is pale in color before cooking. In culinary terms, only flesh from mammals or fowl is classified as red or white. In nutritional science, red meat is defined as any meat that has more of the protein myoglobin than white meat. White meat is defined as non-dark meat from fish or chicken.

<span class="mw-page-title-main">Lutein</span> Yellow organic pigment created by plants

Lutein is a xanthophyll and one of 600 known naturally occurring carotenoids. Lutein is synthesized only by plants, and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach, kale and yellow carrots. In green plants, xanthophylls act to modulate light energy and serve as non-photochemical quenching agents to deal with triplet chlorophyll, an excited form of chlorophyll which is overproduced at very high light levels during photosynthesis. See xanthophyll cycle for this topic.

<span class="mw-page-title-main">Zeaxanthin</span> Chemical compound

Zeaxanthin is one of the most common carotenoids in nature, and is used in the xanthophyll cycle. Synthesized in plants and some micro-organisms, it is the pigment that gives paprika, corn, saffron, goji (wolfberries), and many other plants and microbes their characteristic color.

Megavitamin therapy is the use of large doses of vitamins, often many times greater than the recommended dietary allowance (RDA) in the attempt to prevent or treat diseases. Megavitamin therapy is typically used in alternative medicine by practitioners who call their approach orthomolecular medicine. Vitamins are useful in preventing and treating illnesses specifically associated with dietary vitamin shortfalls, but the conclusions of medical research are that the broad claims of disease treatment by advocates of megavitamin therapy are unsubstantiated by the available evidence. It is generally accepted that doses of any vitamin greatly in excess of nutritional requirements will result either in toxicity or in the excess simply being metabolised; thus evidence in favour of vitamin supplementation supports only doses in the normal range. Critics have described some aspects of orthomolecular medicine as food faddism or even quackery. Research on nutrient supplementation in general suggests that some nutritional supplements might be beneficial, and that others might be harmful; several specific nutritional therapies are associated with an increased likelihood of the condition they are meant to prevent.

Vitamin B<sub>12</sub> deficiency Disorder resulting from low blood levels of vitamin B12

Vitamin B12 deficiency, also known as cobalamin deficiency, is the medical condition in which the blood and tissue have a lower than normal level of vitamin B12. Symptoms can vary from none to severe. Mild deficiency may have few or absent symptoms. In moderate deficiency, feeling tired, headaches, soreness of the tongue, mouth ulcers, breathlessness, feeling faint, rapid heartbeat, low blood pressure, pallor, hair loss, decreased ability to think and severe joint pain and the beginning of neurological symptoms, including abnormal sensations such as pins and needles, numbness and tinnitus may occur. Severe deficiency may include symptoms of reduced heart function as well as more severe neurological symptoms, including changes in reflexes, poor muscle function, memory problems, blurred vision, irritability, ataxia, decreased smell and taste, decreased level of consciousness, depression, anxiety, guilt and psychosis. If left untreated, some of these changes can become permanent. Temporary infertility, reversible with treatment, may occur. A late finding type of anemia known as megaloblastic anemia is often but not always present. In exclusively breastfed infants of vegan mothers, undetected and untreated deficiency can lead to poor growth, poor development, and difficulties with movement.

<span class="mw-page-title-main">Vitamin D</span> Group of fat-soluble secosteroids

Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, along with numerous other biological functions. In humans, the most significant compounds within this group are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol).

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