Why Biological Sex Matters in Research Studies

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“Boys are rotten, made out of cotton. Girls are handy, made out of candy.” While this silly elementary schoolyard rhyme is obviously not accurate, the underlying message is true: Males and females are physiologically different in some ways, particularly when it comes to sex organs and hormones. Until recently, however, the majority of what we know about diseases came from studies done only in men. As researchers begin to include women in studies, they have learned that symptoms of diseases can sometimes present differently and that our sex hormones can play an important role in the protection against or development of disease.

Puberty is an awkward time that many of us would like to forget. But it is also when the production of sex hormones increases. Our organs produce hormones that travel through the blood and act as messengers around the body. During the female reproductive years, estrogen and progesterone rise and fall throughout the monthly menstrual cycle. When women enter menopause, their sex hormone production drops significantly. Estrogen, progesterone, testosterone and other sex hormones are commonly known for their actions during puberty, but they do a lot more.

One research study found that as estrogen rises during the monthly menstrual cycle, female blood vessel health improves as well. Similarly, until menopause, women typically have less heart disease compared to men of the same age. However, after menopause, the risk of heart disease increases. Men also have a decline in hormone production—in this case, testosterone—later in life, which is associated with increased cardiovascular risk. We see sex differences in heart health because men and women produce different amounts of these sex hormones.

Researchers are working to better understand how sex hormones may affect the health of men and women differently. Ongoing studies are looking at how conditions such as kidney disease, heart disease, stroke and diabetes vary between the sexes, especially how hormones may be driving these differences.

Based on the information we already have, it is important to consider both sexes and hormonal status (for example, whether a person is pre- or postmenopause) when conducting research studies. The hope is that as scientists begin to understand more, the future of disease prevention and treatment will be tailored to the patient’s sex.

Casey Derella is a doctoral candidate in the Laboratory of Integrative Vascular and Exercise Physiology at Augusta University in Georgia. She researches how various diseases alter vascular and skeletal muscle function and ultimately contribute to the development of cardiovascular disease.

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