Nutritional epidemiology

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The nutrition pyramid, also known as the food pyramid Nutrition-pyramid.jpg
The nutrition pyramid, also known as the food pyramid

Nutritional epidemiology examines dietary and nutritional factors in relation to disease occurrence at a population level. [1] Nutritional epidemiology is a relatively new field of medical research that studies the relationship between nutrition and health. [2] It is a young discipline in epidemiology that is continuing to grow in relevance to present-day health concerns. [1] 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. [2] Nutritional epidemiology uses knowledge from nutritional science to aid in the understanding of human nutrition and the explanation of basic underlying mechanisms. [3] Nutritional science information is also used in the development of nutritional epidemiological studies and interventions including clinical, case-control and cohort studies. [4] Nutritional epidemiological methods have been developed to study the relationship between diet and disease. Findings from these studies impact public health as they guide the development of dietary recommendations including those tailored specifically for the prevention of certain diseases, conditions and cancers. It is argued by western researchers [1] [5] that nutritional epidemiology should be a core component in the training of all health and social service professions because of its increasing relevance and past successes in improving the health of the public worldwide. [4] However, it is also argued that nutritional epidemiological studies yield unreliable findings as they rely on the role of diet in health and disease, which is known as an exposure that is susceptible to considerable measurement error. [6]

Contents

History of nutritional epidemiology

Nutritional epidemiology started as a subdiscipline of epidemiology in the 1980s [7] before advancing into a core disciple in epidemiology. It deals with the role nutritional exposures play in the occurrence of impaired health conditions. The assessment of these exposures and the investigation of the association between exposure and outcome form the core of nutritional epidemiology. [7] It is through the understanding of how nutrients and vitamins affect deficiency and disease early in the twentieth century that nutritional epidemiology became better established. [8] Later in the twentieth century it gained further significance when the role of exposure in chronic disease became well understood. [8] Since then, the application of information from nutritional epidemiology has led to significant scientific and social breakthroughs. [9] Epidemiological methods have been used for centuries to study the relationship between diet and disease, [10] yet were not considered definitive. Advancements to the ways in which dietary exposures were measured gave rise to the reliability of data. The inclusion of genetic risk factors in models of causation have made nutritional epidemiology an increasingly interdisciplinary field. [11]

Nutritional science

Various medicinal capsules and tablets 201707 medicine mix.svg
Various medicinal capsules and tablets

Nutritional science is a multidisciplinary study area concerned with the role of nutrition in health and disease across the human lifespan. [12] Nutritional epidemiology and nutritional science are two fields that share knowledge about the interactions of nutrients, food consumption, and the human body. [13] An understanding of the principles of nutritional sciences is required to understand nutritional epidemiology. [14] The two fields explore diet-disease relationships to provide preventative measures for the public. [15] Research in nutritional science also provides the basis for food regulations and dietary guidelines. [13] Knowledge from Nutritional science has raised societal awareness about links between food consumption and wellbeing. [12] Examples of some of the successes nutritional science has contributed to findings which include linking folate deficiency to a higher risk of neural tube defects, vitamin C deficiency to scurvy, consumption of trans fat to a higher risk of cardiovascular disease and linking consumption of fish during pregnancy to reduced risk of preterm birth. [16] These occurrences continue to be discovered with increasing scientific information and evidence, leading to more opportunities for successful intervention and prevention. [16]

Nutritional epidemiological studies

Nutritional epidemiological studies form the foundation for nutrition-related discoveries. [6] The studies reveal the relationship between nutrition and health, with a focus on aetiology of chronic disease. [6] They provide a comprehensive view of the way in which diet affects or maintains health and wellbeing in individuals and populations. A prominent controversy lies within the ability to reliably and accurately measure exposures as they are subject to measurement errors and variation. [12] Nutritional epidemiological study designs are required to establish a definitive relationship between diet and disease to be able to develop interventions and policies that will be implemented for the health of the public. [12] There are observational and experimental investigations which have applicable study designs that fall under them including ecological, cross-sectional, cohort, case control, clinical and community trails.[ citation needed ]

Investigators in experimental studies have the control of assigning exposures, whereas in observational studies exposures are observed only with no intervention. [17] Experimental studies can therefore provide stronger evidence for the effect of exposure on outcome, which would otherwise be considered unethical in an observational study as exposure could be harmful. [6] But Observational studies are simpler to carry out and more cost effective. Observational studies are able to detect rare or unusual findings over long periods of time (diet-related diseases develop over time) which would otherwise burden subjects and be expensive in Experimental studies. [17] In nutritional epidemiology, Experimental studies may be used to draw causal conclusions between dietary exposures and health outcomes, [18] however for some diet-disease relations there are ethical considerations. [17] Nutritional policy and procedure decisions are therefore guided by findings from a combination of sources to ensure accuracy, reliability and validity. [18]

The measure of exposure is dependent on the question and study design. [6] It can be objectively or subjectively measured on individuals or populations in the past or present. In nutritional epidemiological studies this refers to factors such as food including nutrients and non-nutrients and the social environment. [19] The effect of these exposures is measured as outcomes. [17] In nutritional epidemiological the outcome is commonly referred to as the disease state or the anthropometric or physiological state under either continuous or discrete variables. The objective of nutritional epidemiological research is to provide scientific evidence to support an understanding of the role of nutrition on the causes and prevention of ill health. [6] It is important to address the factors that affect food supply, including quality, quantity and balance and the factors that affect food after consumption. The development of a specific, feasible and relevant aim of study and target population is the first step in epidemiological research. [19] The second step is the selection and correct use of a method that measures exposure and outcome followed by extensive analysis. Exposure and outcome of interest are measured to enable reliability of the relationship assessed. Studies that are well designed, have a strong foundation, detailed methodology and are governed by ethical principles will have the derived conclusions used to improve health care. All steps require knowledge of past and current literature. [6]

The different nutritional epidemiological study designs offer advantages and limitations in different circumstances.[ citation needed ]

Ecological study

An ecological study is an observational study that studies risk-modifying factors on health outcomes of populations based on their geographical and/or temporal ecological state. Ecological studies are useful in studying patterns of disease in large populations however may not accurately reflect true associations between individuals within those large populations. [20] Ecological studies use geographical information to examine spatial framework of disease and exposure but there is potential for systemic difference in classification language. [17]

Cross-sectional study

A cross-sectional study is an observational-individual study that measures exposure and outcome in the present. In examining the relationship between disease and diet, cross sectional studies provide a snapshot of the frequency of disease in a population at a given point in time. [20] Cross-sectional studies offer advantages such as the ability to measure multiple outcomes and exposures and, in the planning, and allocation of health resources as it assesses the burden of disease in a specified population. The measure of the outcome is however heavily reliant on population responses. Non-response results in responder bias and therefore unreliable results. [17]

Case control study

A case-control study is an observational-individual study that is defined by the outcome (i.e. measures outcomes in the present and past exposure is established). It involves two groups controls and cases (diseased), both which have two treatments; exposed and unexposed. [17] Case-control studies can be used to study diseases that are rare and over long periods of time however are limited to examining one outcome and are also susceptible to the effects of bias if selected control groups are no representative of the population, so give rise to misleading results. [20]

Cohort study

A cohort study is an observational-individual study that measures exposure in the present over long periods of time and the outcome is determined in the future. [20] Cohort studies allow for multiple outcomes to be measure per one exposure. [17] In nutritional epidemiological studies it is advantageous in measuring outcomes that occur after exposure and can measure both incidence and prevalence. Cohort studies are however costly and time consuming. [18] As outcome is determined in the future, any issues pertaining to the collection of information or confounders cannot be resolved back in time.[ citation needed ]

Clinical and community trails

Clinical and community trails are experimental studies that involve active intervention in either individuals (clinical) or populations (community). Clinical trials often involve test and procedures carried on subjects placed in different treatment groups. [17] Clinical trials allow for the evaluation of new therapies, drugs and procedures. Clinical trials however risk subject to experience side effects and inadvertent harm from the intervention therefore should only be considered when supporting evidence is strong. [20] Community trials involve assigning groups of individuals with and without disease to different interventions. This allows for larger scale findings however does not account for individual variability. [17]

Social impact

The impact nutritional epidemiology had in the past has led to social, physical and economic changes. Nutritional epidemiological findings guide dietary recommendations including the prevention of certain disease and cancers. [1] They play a role in policies on diet and health given the works are published based on grounding evidence. [5] The observational findings allowed for health interventions such as the fortification of foods and limits/bans of certain substances from food. [5] These implemented changes have since enhanced human health and wellbeing by means of prevention and improvement. Research suggest its impact specifically on cancer patients has been promising. [1] The nutritional support to some provides relief of side effects, improves response to therapy and reduces the risk of cancer reoccurring, all of which enhance the quality of life for cancer patients. [1] Progressive impacts have also been seen on a variety of infectious diseases, chronic disease, and congenital malformations, [5] ultimately elevating the burden on the healthcare system and striving for optimal function.

A Nutritional Label on Food Package Palmini Nutrition Label.jpg
A Nutritional Label on Food Package

Nutritional epidemiology is the scientific basis upon which public health nutrition is built. [6] Nutritional epidemiology aims to deliver knowledge on how to cope with an imbalance between nutrients that causes illness such as anaemia, goitre wasting and stunting. The understanding of the characteristics of exposures require measurement to understand the diet–disease relationship. The ability to relate exposure to steps in the causal pathway improves the value of findings in relation to public health recommendations. [17]

See also

Related Research Articles

<span class="mw-page-title-main">Epidemiology</span> Study of health and disease within a population

Epidemiology is the study and analysis of the distribution, patterns and determinants of health and disease conditions in a defined population.

The science of epidemiology has matured significantly from the times of Hippocrates, Semmelweis and John Snow. The techniques for gathering and analyzing epidemiological data vary depending on the type of disease being monitored but each study will have overarching similarities.

A cohort study is a particular form of longitudinal study that samples a cohort, performing a cross-section at intervals through time. It is a type of panel study where the individuals in the panel share a common characteristic.

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

The Mediterranean diet is a diet inspired by the eating habits and traditional food typical of southern Spain, southern Italy, and Crete, 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.

<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, 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.

A case–control study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case–control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have the condition with patients who do not have the condition but are otherwise similar. They require fewer resources but provide less evidence for causal inference than a randomized controlled trial. A case–control study is often used to produce an odds ratio. Some statistical methods make it possible to use a case–control study to also estimate relative risk, risk differences, and other quantities.

<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. Plant-based diets encompass 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 and seeds. They do not need to be vegan or vegetarian, but are defined in terms of 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">Mendelian randomization</span> Statistical method in genetic epidemiology

In epidemiology, Mendelian randomization is a method using measured variation in genes to examine the causal effect of an exposure on an outcome. Under key assumptions, the design reduces both reverse causation and confounding, which often substantially impede or mislead the interpretation of results from epidemiological studies.

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

Dietary factors are recognized as having a significant effect on the risk of cancers, with different dietary elements both increasing and reducing risk. Diet and obesity may be related to up to 30–35% of cancer deaths, while physical inactivity appears to be related to 7% risk of cancer occurrence.

Environmental epidemiology is a branch of epidemiology concerned with determining how environmental exposures impact human health. This field seeks to understand how various external risk factors may predispose to or protect against disease, illness, injury, developmental abnormalities, or death. These factors may be naturally occurring or may be introduced into environments where people live, work, and play.

Molecular epidemiology is a branch of epidemiology and medical science that focuses on the contribution of potential genetic and environmental risk factors, identified at the molecular level, to the etiology, distribution and prevention of disease within families and across populations. This field has emerged from the integration of molecular biology into traditional epidemiological research. Molecular epidemiology improves our understanding of the pathogenesis of disease by identifying specific pathways, molecules and genes that influence the risk of developing disease. More broadly, it seeks to establish understanding of how the interactions between genetic traits and environmental exposures result in disease.

<span class="mw-page-title-main">Western pattern diet</span> Modern dietary pattern

The Western pattern diet is a modern dietary pattern that is generally characterized by high intakes of pre-packaged foods, refined grains, red meat, processed meat, high-sugar drinks, candy and sweets, fried foods, industrially produced animal products, butter and other high-fat dairy products, eggs, potatoes, corn, and low intakes of fruits, vegetables, whole grains, pasture-raised animal products, fish, nuts, and seeds.

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. 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. 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.

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.

Population impact measures (PIMs) are biostatistical measures of risk and benefit used in epidemiological and public health research. They are used to describe the impact of health risks and benefits in a population, to inform health policy.

<span class="mw-page-title-main">Salt and cardiovascular disease</span> Association between salt consumption and cardiovascular disease

Salt consumption has been extensively studied for its role in human physiology and impact on human health. Chronic, high intake of dietary salt consumption is associated with hypertension and cardiovascular disease, in addition to other adverse health outcomes. Major health and scientific organizations, such as the World Health Organization, US Centers for Disease Control and Prevention, and American Heart Association, have established high salt consumption as a major risk factor for cardiovascular diseases and stroke.

Lawrence J. Appel is the C. David Molina Professor of Medicine and Director of the Welch Center for Prevention, Epidemiology and Clinical Research at Johns Hopkins University, a joint program of the Johns Hopkins University School of Medicine and the Bloomberg School of Public Health. Dr. Appel is a primary care internist who holds a primary appointment in the Department of Medicine with joint appointments in the Department of Epidemiology, International Health, and Nursing. In addition, he directs the ProHealth Clinical Research Unit. The focus of his career is the conduct of clinical, epidemiologic, and translational research pertaining to the prevention and control of high blood pressure, cardiovascular-kidney diseases, and other chronic conditions, primarily through nutrition-based interventions.

Cheryl Ann Marie Anderson is an American epidemiologist. Anderson is a professor at and founding Dean of the University of California San Diego Herbert Wertheim School of Public Health and Human Longevity Science. Anderson's research focus is on nutrition and chronic disease prevention in under-served human populations.

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