5 Lessons from the Largest Scientific Study on Women, Ever

By Susan E. Matthews, Everyday Health

White men have been the primary subjects of scientific research for most of medical history, making it pretty difficult to know how to treat conditions that affect other populations, particularly women. Take menopause: For years, doctors prescribed long-term use of hormones estrogen and progestin to help women manage symptoms during and after menopause because it helped women feel better. But in 1991, researchers wanted a definitive answer as to whether hormones used to ease menopause's symptoms were helping women more than they were hurting them. So, the National Institutes of Health launched the largest study ever focused exclusively on women to answer that question.

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Dubbed the Women's Health Initiative (WHI), the research project recruited 68,132 postmenopausal women to participate. They were divided into groups, some taking just estrogen, some taking estrogen and progestin, and some taking placebos. After over a decade of observation, the researchers stopped the trials early, in 2002 and 2004, because it was so clear that hormones posed serious health risks to the women. However, researchers have continued to follow up with these women in the years since, and have also tested other health interventions on the group, including low-fat diets and taking vitamin D and calcium. In 1998, an observational component of the WHI launched, with another 93,676 participants, to study even more aspects of women's health. Much of the data collected over the years is now accessible to other researchers, too.

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This has created a glut of women-specific health information that has paid off in big ways. In fact, the findings from the WHI have prompted a net economic return of $37.1 billion dollars, or $140 for each dollar that was spent on the trial itself, according to a new paper published in the Annals of Internal Medicine. That's because the results have led to better treatment and care for millions of women, decreasing healthcare spending and increasing quality of life.

Here are some of the most important WHI findings:

1. You probably shouldn't take hormones for longer than you have to. Long-term use of estrogen and progestin increases the risk of breast cancer, heart attack, stroke, and blood clots, though it decreased the risk of hip fractures and colon cancer in the main WHI trial. While these results have caused doctors to largely stop prescribing long-term hormone replacement, individuals are encouraged to make a personal decision based on their own risk factors. For example, if a woman has a very low family history of breast cancer and cardiovascular disease, but a high risk of colon cancer and osteoporosis, she may choose to take the hormones, which are thought to be safe when prescribed for just a short time around menopause, to manage symptoms. They may also extend the life expectancy for women who have had hysterectomies, the data revealed, so be sure to talk to your doctor about your specific needs.

2. Low-fat diets are good, but not enough to reduce your risk of some cancers or cardiovascular disease. The researchers asked some of the participants to eat a low-fat diet, and then compared how this affected their risk of various diseases. They found that a low-fat diet alone was not enough to significantly impact women's risk of cardiovascular disease, breast cancer, or colorectal cancer, according to the results published in JAMA. The researchers concluded that more dramatic lifestyle changes, including increased exercise, might be necessary to affect risk of developing these diseases.

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3. Taking vitamin D and calcium may not be worth it. Some of the women in the study were given calcium and vitamin D supplements, while others were not. The results showed that the supplements did increase the bone density in the hip, but they didn't significantly decrease the number of hip fractures the women experienced. Nor did taking the supplements lower the risk of colorectal cancer, according to the paper published in the New England Journal of Medicine. They did, however, increase the risk of kidney stones.

RELATED: Rethinking Calcium Supplements for Women

4. Ditch diet soda. Post-menopausal women who reported drinking two or more diet sodas per day had a higher risk of heart attack, stroke, and other heart problems, research from the WHI showed. While the researchers couldn't show a direct connection, there are plenty of other reasons to avoid fake sugar.

5. If you're at high risk for melanoma, aspirin might help. Researchers analyzed the data from the WHI observational study, and found that women who took aspirin regularly had a 20 percent lower risk of melanoma than women who did not. The correlation was strong - the longer the women took the drug, the lower their risk. Aspirin comes with its own benefits (preventing subsequent heart problems) and harms (increased risk of bleeding), so talk to your doctor before adding it to your routine.

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This article originally appeared on EverydayHealth.com: 5 Lessons From the Largest Scientific Study on Women, Ever