A 60-Year Study of Health and Nutrition in the U.S., Explained
Illustrations by Israel Vargas
By the late 1960s, lead had been recognized as a toxic substance for over a thousand years. The heavy metal made the mind “give way,” wrote the Greek physician Dioscorides in the 1st Century AD; Vitruvius, Julius Caesar’s engineer, wrote hundreds of years later that lead aqueducts made water “injurious.” And yet more than halfway through the 20th century, American cars used leaded gasoline to boost octane, and in the soldering of tin cans that held food and soft drinks. The deadly practice was halted in large part by a series of studies that continues today — and that most Americans have still never heard of.
“It should be the most famous story about the study, and yet most people don’t know,” said Chia-Yih Wang, a nutritional epidemiologist and a project lead at the Center for Disease Control and Prevention’s National Center for Health Statistics (NCHS), the government agency that oversees the study. “NHANES was the first time we had evidence that Americans had too much lead in their blood.” More importantly, the findings of NHANES — the National Health and Nutrition Examination Survey — led congress and the EPA to take action, decreasing the prevalence of elevated lead levels in the blood more than 70 percent since the 1970s.
NHANES is a long-running public health research program that has had a profound effect on our understanding of health and wellness in America and has shaped domestic policy related to both. NHANES is unique among health studies in the U.S., not just because its studies have spanned six decades, but also because it combines interviews covering an enormous range of topics, including acculturation, air quality, immunization, oral health, and occupation, with physical examinations that measure balance, blood pressure, muscle strength, vision, and much more. For example, from recent NHANES data we learned that more than half of American adults take supplements and that cigarette smoking among adults is at an “all-time low,” having declined by 67 percent since 1965.
Today, the studies that make up NHANES continue to change. And soon, they might include a whole other kind of study, one aimed at following the progress of our health, that might reveal new clues as to how and why Americans face chronic diseases, and how they age. Here, we unpack its history, contributions to human healthcare and policy, and future implications.
NHANES and its precursors have been surveying health in the U.S. for over 60 years. And its roots go even deeper. In 1935 and 1936, the National Health Survey set out on the largest survey of its kind, to examine the health of over 737,000 urban households in America; the data collected was used for hundreds of papers and to inform America’s growing healthcare policies. But for the next twenty years, the 1935 study was the only large-scale effort to survey health across the country.
In 1956, President Dwight Eisenhower signed into law the National Health Survey Act, which authorized the Surgeon General “to make, by sampling or other appropriate means, surveys and special studies of the population of the United States to determine the extent of illness and disability and… to develop and test new or improved methods for obtaining current data on illness and disability or related information.” This data was to be made available not only to government agencies concerned with public health but also to scientists and public and non-profit institutions.
The first three studies, called National Health Examination Survey I, II, and III, took place between 1960 and 1970 and each surveyed around 7,500 individuals, a sampling meant to give insight into America’s roughly 111,000,000 citizens at the time. NHES I surveyed Americans aged 18 to 79 for chronic diseases, including psychological distress (“Have you ever had a nervous breakdown?”), cardiovascular disease (“Heart pain — duration?”), arthritis (“Joint tenderness?”), and diabetes (“Was your last meal bread, potatoes, cereal?”). NHES II and III focused on childhood development in children, first between the ages of 6 and 11, then between the ages of 12 and 17. Each participant was surveyed once, answering questions, providing health records, and submitting to physical examinations.
The next four surveys, which took place in three- to four-year spans between 1971 and 1994, added a significant new focus, nutrition, which had emerged as an important variable in relation to health and disease. So NHES became NHANES, the National Health and Nutrition Examination Survey.
Each of the four NHANES studies focused on upwards of 16,000 individuals, and eventually expanded those surveyed to individuals aged two months old and up. Between 1971 and 1980, NHANES I and II were conducted similarly, and across a broad range of Americans, surveying for a broad variety of health and nutritional data; between 1982 and 1984, HHANES (Hispanic Health and Nutrition Examination Survey) focused more heavily on the three largest Hispanic subgroups in the U.S., Mexican Americans, Cuban Americans, and Puerto Ricans; NHANES III, conducted from 1988 to 1994, continued the heightened level of study on minorities, and added further examination on environmental effects, including pesticide exposure and carbon monoxide in the blood.
Since 1999, NHANES data has been continuously collected, surveying around 7,000 new individuals annually from 15 different counties across the United States. In the modern system, a computer algorithm helps members of the NCHS who run the survey select who should be included, so that the survey reflects America’s diverse population; currently, the population of Hispanics, non-Hispanic black, non-Hispanic Asian, low-income whites, and people older than 80 are over-surveyed to ensure that those populations’ sample size is large enough to study. Those selected in the survey receive a home visit, where they are interviewed on a broad range of health, nutrition, cultural, and socioeconomic questions. Then, they visit a mobile examination center (MEC), a customized double-wide trailer where researchers are able to run them through a battery of tests.
The modern, continuous form of NHANES has been particularly successful given the flexibility it provides surveyors and researchers. “We get the chance to study emerging health issues, and that type of flexibility is important for the design of the study,” Wang said. Continuity also means that researchers can combine many different years of data collection for larger samples and to see changing trends. Research from recent years has made major impacts on health in America. The data collected helped to create the growth charts found in pediatric doctors’ offices across the country; its surveys on diet have been used as a baseline for understanding what Americans eat, and solving deficiencies in vitamins and minerals; findings related to childhood obesity have led to a number of programs aimed at childhood nutrition and exercise, and have similarly identified diabetes as a major epidemic; continued monitoring of cholesterol levels have shown a decrease in problematic high cholesterol, signaling the effectiveness of modern treatment.
But NHANES, though now continuously surveying Americans, still offers single, frozen moments in the lives of all different kinds of Americans: a cross-section of health. “The study gives us a snapshot of health and nutrition status of the country, every year,” Wang said. Increasingly, Wang and others at government health agencies find themselves concerned with increasing trends in obesity and chronic diseases — diabetes, cancer, and heart disease, for instance, all of which are tied to the increasing lifespans of Americans, who are living longer but are not healthier in their old age. Approximately six in 10 adult Americans are living with chronic diseases, and that number is expected to continue to increase, stressing the country’s healthcare system and lowering quality of life for a huge percentage of the country.
“This kind of increased prevalence of chronic diseases is an important health issue,” Wang said. “If we can follow up with previous NHANES participants in a longitudinal setting, that would allow us to identify and monitor more information relating to the factors that cause chronic disease. And because we make that data publicly available, the use of that data would be large-scale for research communities.”
A longitudinal study represents one of science’s great feats of observation. The data related to a group of individuals are observed and recorded over a long period of time. The longitudinal style of study is most frequently used in psychology, sociology, and medicine.
Longitudinal studies, in which data related to a group of individuals are observed and recorded over a long period of time, offer a powerful tool in researching chronic diseases, mortality, and aging. These studies represent one of science’s great feats of observation. Longitudinal studies don’t just give researchers raw data; they provide a timeline of data, dots that can then be connected to tell a story about not just how healthy a person is, but why they might be healthy or not healthy.
In observational longitudinal studies, participants and their exposures and outcomes are tracked but not manipulated by researchers, as opposed to experiments like a clinical trial, in which a group of participants is exposed to a treatment and another group acts as a control. Because of their passive nature and lack of constants, longitudinal studies have less ability to detect causal relationships than do controlled trials.
Longitudinal studies are also by their very nature expensive and difficult to maintain, making successful ones, of particular note to the scientific community. Around the world, stand-out studies like the Dunedin Multidisciplinary Health and Development Study and the UK Biobank have provided lifetimes of raw data for tens and even hundreds of thousands of people. That data has been used by researchers to find connections between cannabis use and health, the prevalence of mental illness in young people, and even change criminal justice policy related to juvenile delinquency.
Wang and others believe that adding a longitudinal element to NHANES could provide more answers on issues like obesity and diabetes in Americans. Their plan is to conduct follow-up research on NHANES participants from the last three to 10 years, some 22,000 adult individuals. “Now, we know how many people in the United States have diabetes,” Wang said. “But in a longitudinal follow-up study, we can ask, ‘What are the factors related to this increase?’ Some people we studied ten years ago will have developed diabetes, and some haven’t. We can compare baseline factors to see if those two groups ate or exercised differently, or if they have different healthcare.” Longitudinally, they’ll be seeing aging, and the slow creep of chronic disease, in action for the first time. And given the dramatic increase in older Americans, data specific to an aging population has major implications for health care needs, public policy, and research priorities on a national scale.
At the same time, longitudinal studies face unique hurdles, including being both very expensive and difficult to carry out. While NHANES did conduct a follow-up study in the 1980s, since then, the response rate to major federal surveys has declined across the board. Retaining participants in longitudinal studies is a notorious challenge — one NHANES may see compounded because it’s trying to transform a one-time study into a longitudinal one. “We set out to be a snapshot of the nation,” Wang said. “So we’ll be picking up some relationships three to ten years later, showing up at peoples’ doors and saying, ‘Hey, remember us? Can you do this again?’”
So far, Wang and her colleagues have launched a feasibility study to see whether a longitudinal follow-up would work. Of the 800 prior NHANES participants they reached out to, around 70 percent participated in a home interview; of those participants, over 90 percent agreed to complete the accompanying home examination. Numbers like these beg the question: What’s next for an NHANES longitudinal study that could provide more data about Americans than ever before about chronic disease and aging?
“To do this kind of study, the research needed is quite large,” Wang said. “We just wanted to start somewhere. Which is why we are thinking about this as a one-shot follow-up. Whether there is a potential to do multiple follow-ups on the same cohort, or routine follow-ups on a future NHANES study, really depends on those budgets and resources.” In the meantime, the NCHS should have a paper out about their NHANES longitudinal feasibility study sometime this year, which will signal whether they’ll be able to move forward with this important study on how Americans age.
A 60-Year Study of Health and Nutrition in the U.S., Explained
Research & References of A 60-Year Study of Health and Nutrition in the U.S., Explained|A&C Accounting And Tax Services
Source
0 Comments