Ecological study

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In epidemiology, ecological studies are used to understand the relationship between outcome and exposure at a population level, where 'population' represents a group of individuals with a shared characteristic such as geography, ethnicity, socio-economic status of employment. [1] What differentiates ecological studies from other studies is that the unit analysis being studied is the group, therefore inferences cannot be made about individual study participants. [2] On the other hand, details of outcome and exposure can be generalized to the population being studied. Examples of such studies include investigating associations between units of grouped data, such as electoral wards, regions, or even whole countries. [3]

Contents

Study Design

Generally, three different designs can be used to conduct ecological studies depending on the situation. Such studies may compare populations or groups using a multiple-group design, periods of time using a time-trend design, or groups and time using a mixed design. [1] [4]

Notable examples

Cholera study

The study by John Snow regarding a cholera outbreak in London is considered the first ecological study to solve a health issue. He used a map of deaths from cholera to determine that the source of the cholera was a pump on Broad Street. He had the pump handle removed in 1854 and people stopped dying there. [5] It was only when Robert Koch discovered bacteria years later that the mechanism of cholera transmission was understood. [6]

Diet and cancer

Dietary risk factors for cancer have also been studied using both geographical and temporal ecological studies. Multi-country ecological studies of cancer incidence and mortality rates with respect to national diets have shown that some dietary factors such as animal products (meat, milk, fish and eggs), added sweeteners/sugar, and some fats appear to be risk factors for many types of cancer, while cereals/grains and vegetable products as a whole appear to be risk reduction factors for many types of cancer. [7] [8] Temporal changes in Japan in the types of cancer common in Western developed countries have been linked to the nutrition transition to the Western diet. [9]

UV radiation and cancer

An important advancement in the understanding of risk-modifying factors for cancer was made by examining maps of cancer mortality rates. The map of colon cancer mortality rates in the United States was used by the brothers Cedric and Frank C. Garland to propose the hypothesis that solar ultraviolet B (UVB) radiation, through vitamin D production, reduced the risk of cancer (the UVB-vitamin D-cancer hypothesis). [10]

Diet and Alzheimer's

Links between diet and Alzheimer's disease have been studied using both geographical and temporal ecological studies. The first paper linking diet to risk of Alzheimer's disease was a multi-country ecological study published in 1997. [11] It used prevalence of Alzheimer's disease in 11 countries along with dietary supply factors, finding that total fat and total energy (caloric) supply were strongly correlated with prevalence, while fish and cereals/grains were inversely correlated (i.e., protective). Diet is now considered an important risk-modifying factor for Alzheimer's disease. [12] Recently it was reported that the rapid rise of Alzheimer's disease in Japan between 1985 and 2007 was likely due to the nutrition transition from the traditional Japanese diet to the Western diet. [13]

UV radiation and influenza

Another example of the use of temporal ecological studies relates to influenza. John Cannell and associates hypothesized that the seasonality of influenza was largely driven by seasonal variations in solar UVB doses and calcidiol levels. [14] A randomized controlled trial involving Japanese school children found that taking 1000 IU per day vitamin D3 reduced the risk of type A influenza by two-thirds. [15]

Advantages and drawbacks

Ecological studies are particularly useful for generating hypotheses since they can use existing data sets and rapidly test the hypothesis. The advantages of the ecological studies include the large number of people that can be included in the study and the large number of risk-modifying factors that can be examined.[ citation needed ]

The term "ecological fallacy" means that risk-associations apparent between different groups of people may not accurately reflect the true association between individuals within those groups. Ecological studies should include as many known risk-modifying factors for any outcome as possible, adding others if warranted. Then the results should be evaluated by other methods, using, for example, Hill's criteria for causality in a biological system.[ citation needed ]

Related Research Articles

Vitamin E is a group of eight compounds related in molecular structure that includes 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, 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.

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">Cholecalciferol</span> Vitamin D3, a chemical compound

Cholecalciferol, also known as vitamin D3 or colecalciferol, is a type of vitamin D that is produced by the skin when exposed to UVB light; it is found in certain foods and can be taken as a dietary supplement.

<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.

<span class="mw-page-title-main">Multivitamin</span> Dietary supplement containing vitamins

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 as a category of food.

<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">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">Healthy diet</span> Type of diet

A healthy diet is a diet that maintains or improves overall health. A healthy diet provides the body with essential nutrition: fluid, macronutrients such as protein, micronutrients such as vitamins, and adequate fibre and food energy.

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.

The European Prospective Investigation into Cancer and Nutrition (EPIC) study is a Europe-wide prospective cohort study of the relationships between diet and cancer, as well as other chronic diseases, such as cardiovascular disease. With over half a million participants, it is the largest study of diet and disease to be undertaken.

<span class="mw-page-title-main">Diet and cancer</span> Connections between dietary habits and cancer

Many dietary recommendations have been proposed to reduce the risk of cancer, few have significant supporting scientific evidence. Obesity and drinking alcohol have been correlated with the incidence and progression of some cancers. Lowering the consumption of sweetened beverages is recommended as a measure to address obesity.

The chronic endothelial injury hypothesis is one of two major mechanisms postulated to explain the underlying cause of atherosclerosis and coronary heart disease (CHD), the other being the lipid hypothesis. Although an ongoing debate involving connection between dietary lipids and CHD sometimes portrays the two hypotheses as being opposed, they are in no way mutually exclusive. Moreover, since the discovery of the role of LDL cholesterol (LDL-C) in the pathogenesis of atherosclerosis, the two hypotheses have become tightly linked by a number of molecular and cellular processes.

<span class="mw-page-title-main">Vitamin D deficiency</span> Human disorder

Vitamin D deficiency or hypovitaminosis D is a vitamin D level that is below normal. It most commonly occurs in people when they have inadequate exposure to sunlight, particularly sunlight with adequate ultraviolet B rays (UVB). Vitamin D deficiency can also be caused by inadequate nutritional intake of vitamin D; disorders that limit vitamin D absorption; and disorders that impair the conversion of vitamin D to active metabolites, including certain liver, kidney, and hereditary disorders. Deficiency impairs bone mineralization, leading to bone-softening diseases, such as rickets in children. It can also worsen osteomalacia and osteoporosis in adults, increasing the risk of bone fractures. Muscle weakness is also a common symptom of vitamin D deficiency, further increasing the risk of falls and bone fractures in adults. Vitamin D deficiency is associated with the development of schizophrenia.

A health claim found on a food labels and in food marketing is a claim by a food manufacturer that their product will reduce the risk of developing a disease or condition.

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

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

The Bradford Hill criteria, otherwise known as Hill's criteria for causation, are a group of nine principles that can be useful in establishing epidemiologic evidence of a causal relationship between a presumed cause and an observed effect and have been widely used in public health research. They were established in 1965 by the English epidemiologist Sir Austin Bradford Hill.

<span class="mw-page-title-main">Nutritional epidemiology</span> Field of medical research on disease and diet

Nutritional epidemiology examines dietary and nutritional factors in relation to disease occurrence at a population level. Nutritional epidemiology is a relatively new field of medical research that studies the relationship between nutrition and health. It is a young discipline in epidemiology that is continuing to grow in relevance to present-day health concerns. Diet and physical activity are difficult to measure accurately, which may partly explain why nutrition has received less attention than other risk factors for disease in epidemiology.

References

  1. 1 2 Carneiro, Ilona. (2011). Introduction to epidemiology. Howard, Natasha. (2nd ed.). Maidenhead, Berkshire: Open University Press. p. 76. ISBN   978-0-335-24462-1. OCLC   773348873.
  2. ↑ Motulsky, Harvey (2018). Intuitive biostatistics : a nonmathematical guide to statistical thinking (Fourth ed.). New York. p. 477. ISBN   978-0-19-064356-0. OCLC   1006531983.{{cite book}}: CS1 maint: location missing publisher (link)
  3. ↑ Bruce, Nigel, 1955- (29 November 2017). Quantitative methods for health research : a practical interactive guide to epidemiology and statistics. Pope, Daniel, 1969-, Stanistreet, Debbi, 1963- (Second ed.). Hoboken, NJ. p. 82. ISBN   978-1-118-66526-8. OCLC   992438133.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  4. ↑ Morgenstern, Hal (1995). "Ecologic Studies in Epidemiology: Concepts, Principles, and Methods". Annual Review of Public Health. 16 (1): 61–81. doi: 10.1146/annurev.pu.16.050195.000425 . ISSN   0163-7525. PMID   7639884.
  5. ↑ Newsom, 2006
  6. ↑ Kaufmann SH; Schaible UE (2005). "100th anniversary of Robert Koch's Nobel Prize for the discovery of the tubercle bacillus". Trends Microbiol. 13 (10): 469–75. doi:10.1016/j.tim.2005.08.003. PMID   16112578.
  7. ↑ Armstrong B; Doll R (1975). "Environmental factors and cancer incidence and mortality in different countries, with special reference to dietary practices". Int J Cancer. 15 (4): 617–31. doi:10.1002/ijc.2910150411. PMID   1140864. S2CID   2595273.
  8. ↑ Grant WB (2014). "A multicountry ecological study of cancer incidence rates in 2008 with respect to various risk-modifying factors". Nutrients. 6 (1): 163–189. doi: 10.3390/nu6010163 . PMC   3916854 . PMID   24379012.
  9. ↑ Tominaga S; Kuroishi T (1997). "An ecological study on diet/nutrition and cancer in Japan". Int J Cancer. 71 (Suppl 10): 2–6. doi: 10.1002/(sici)1097-0215(1997)10+<2::aid-ijc2>3.3.co;2-0 . PMID   9209011.
  10. ↑ Garland CF; Garland FC (1980). "Do sunlight and vitamin D reduce the likelihood of colon cancer?". Int J Epidemiol. 9 (3): 227–31. doi:10.1093/ije/9.3.227. PMID   7440046.
  11. ↑ Grant WB (1997). "Dietary Links to Alzheimer's Disease" (PDF). Alzheimer's Disease Review. 2: 42–57. Archived from the original (PDF) on 2014-06-05. Retrieved 2014-01-27.
  12. ↑ Devanand D; Lee J; Luchsinger J; Manly J; Marder K; Mayeux R; Scarmeas N; Schupf N; Stern Y (2013). "Lessons from epidemiologic research about risk factors, modifiers, and progression of late onset Alzheimer's Disease in New York City at Columbia University Medical Center". J Alzheimers Dis. 33 (Suppl 1): S447-55. doi:10.3233/JAD-2012-129041. PMC   4149254 . PMID   22836187.
  13. ↑ Grant WB (2014). "Trends in diet and Alzheimer's disease during the nutrition transition in Japan and developing countries". J Alzheimers Dis. 38 (3): 611–20. doi:10.3233/JAD-130719. PMID   24037034.
  14. ↑ Cannell JJ; Vieth R; Umhau JC; Holick MF; Grant WB; Madronich S; Garland CF; Giovannucci E (2006). "Epidemic influenza and vitamin D". Epidemiol Infect. 134 (6): 1129–40. doi:10.1017/S0950268806007175. PMC   2870528 . PMID   16959053.
  15. ↑ Urashima M; Segawa T; Okazaki M; Kurihara M; Wada Y; Ida H (2010). "Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren". Am J Clin Nutr. 91 (5): 1255–60. doi: 10.3945/ajcn.2009.29094 . PMID   20219962.
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