Associate Professor of Medicine, Brigham and Women’s Hospital, Boston
The Nurses Health Study (NHS) is one of the greatest health surveys ever attempted. Begun in 1976, the NHS was originally intended to study the long-term effects of birth control pills. Researchers asked a group of 121,700 women—all registered nurses between the ages of 30 and 55—to fill out detailed questionnaires about their medications, lifestyle, and health. In 1980 the study was expanded to include information on diet.
The study’s creators guessed that nurses, given their medical training, would be better at answering detailed questionnaires than the general public would be. And because the women were all in the same profession, factors that usually muddy the statistical waters in huge surveys like this—such as income, education, and access to health care—could be controlled. Every two years, the original participants were sent another questionnaire to fill out, tracking their health as they aged. Participation was excellent: More than 90 percent of the nurses have kept up with the questionnaires over the years. A similar study, the Physicians’ Health Study (PHS), was launched in 1981. The PHS surveyed more than 20,000 male doctors, giving epidemiologists a way to compare women and men.
As time went on, scientists came up with new questions that the people who created the survey never imagined. One of the most important: how aging changes the brain over time. In the 1990s, neuroepidemiologist Francine Grodstein, MD, began plumbing the NHS and PHS data to figure out how things like cardiovascular disease and diabetes affect women’s brains as they age. First, though, she had to come up with a way to measure cognitive function—broadly, brain health—among thousands of NHS participants living all over the country.
The solution, it turned out, was simple: “We do neuropsychological testing by telephone,” says Grodstein, a faculty member at both Harvard University Medical School and Brigham and Women’s Hospital in Boston. Between 1995 and 2007, NHS staffers contacted almost 20,000 women over 70, along with more than 5,000 men who were part of the PHS.
The goal was to get a baseline measure of their cognitive function. The tests are simple: Participants might be read a list of 10 words and asked to repeat them, for example, or to name as many animals as possible in a minute. Every two years, researchers called the women back for more questions. Over the years, their performance on the tests (dubbed the Telephone Interview for Cognitive Status, or TICS) has formed a new source of data on brain health.
Grodstein’s baseline results alone were remarkable. In a study she published in 2001 in the journal Diabetes Care, she found that women with type 2 diabetes were twice as likely to have low scores on the telephone tests as women without diabetes. To find out why, Grodstein turned to the American Diabetes Association, which gave her a clinical research grant to look at the relationships between diabetes and memory loss in women.
There were good reasons to believe that women with diabetes would be more vulnerable to memory loss as they aged. “We know that people with diabetes have a greater risk of cardiovascular disease compared to people without diabetes,” Grodstein says. And the risk for women increases much more than the risk for men does when diabetes enters the picture. If she could prove that memory loss in older women with diabetes follows the same pattern, it would be a good indicator that there were links between memory loss, diabetes, and heart health.
But it turned out that the differences in rates of memory decline were about the same for women with and without diabetes as for men with and without diabetes. This suggested that, unlike cardiovascular disease, diabetes does not confer a higher risk of memory loss on women than men. “We’re still looking for those additional lifestyle factors, like physical activity, that might affect memory in people with diabetes.”
She has found at least one rule that seems to apply to both genders: Stay away from trans fats, the “bad fats” that are often found in deep fryers and margarine tubs. “The higher your intake of trans fats, the more memory loss,” she says. “We looked at other types of fats too, and the more good fats—mono- or polyunsaturated fats—you eat, the better your memory.”
Grodstein plans to continue combing through the data to see what else might help women with diabetes preserve their memory as they get older. With the help of tens of thousands of nurses and doctors dedicated to helping the cause of medical research long after they’ve retired, she may find some answers.