Women are historically underrepresented in medical research.
The nonprofit AAMC reports doctors often viewed men’s bodies as the “norm” and women’s bodies as atypical, even though women make up almost half the world’s population and have outnumbered men in the United States since 1946.
Even today, researchers avoid using female mice in medical studies, in part because they worry that their changing hormones and reproductive cycles could interfere with research results.
“This may contribute to health care disparities, as biological sex can play a role in physiological, metabolic, hormonal, and even cellular differences that can influence how diseases present,” the AAMC reports.
Unfortunately, there are a number of diseases and other medical conditions that affect women more, if not also differently, than men. Here are a few, plus what researchers understand about them thus far.
Alzheimer’s disease
Nearly two-thirds of the 5 million Americans with an Alzheimer’s diagnosis are women, the University of Southern California (USC) reports. Although the difference is stark, researchers aren’t quite sure of the reason for it.
Christian Pike, a professor of gerontology at USC, is studying the gene for apolipoprotein E-4 (APOE4), which increases inflammation in the brain.
Having APOE4 raises a person’s risk of developing Alzheimer’s, but the increased risk is worse for women than men.
If women have one APOE4 gene, their risk of Alzheimer’s is about four times higher. With two copies of the gene, the risk is about 10 times higher. But for men, having one APOE4 gene doesn’t really raise their risk, and having two makes it about four times higher.
Multiple sclerosis
Multiple sclerosis (MS) is a chronic autoimmune condition that affects the nerves in the spinal cord and brain. It strikes four times as many women as men.
The cause of MS is currently unknown, but researchers at the Johns Hopkins Multiple Sclerosis Center are seeking to understand it better. Smoking and stress have been identified as risk factors, and studies are increasingly also pointing to estrogen, vitamin D deficiency, inflammation and obesity.
Researchers note that prior to puberty, the difference between the rate of MS in male and female children isn’t wide. However, that changes after puberty — indicating that hormones may play an important role.
Also, women typically carry more fat on their bodies than men, and obesity rates among women are higher. Carrying more fat, especially around the belly, is linked to an increase in inflammation, which is associated with MS.
Gallstones
Women between the ages of 20 and 60 are three times more likely than men to develop gallstones, which occur in up to 20% of American women by age 60.
The gallbladder, a small organ that sits behind the liver, stores and releases bile, which helps break down fat in foods for digestion. Gallstones are solid lumps that form when bile in the gallbladder crystallizes. They’re made mostly from cholesterol.
A buildup of gallstones can result in pain, nausea, vomiting, jaundice and fever or chills.
One of the factors that can increase a person’s risk for gallstones is having been through multiple pregnancies.
The biggest reason for the disparity between men and women, however, is hormones. Estrogen elevates cholesterol levels in bile, and progesterone slows down the emptying of the gallbladder, both of which contribute to the development of gallstones.
Lupus
About 90% of people with the autoimmune disease lupus, which can affect any part of the body, are women.
The reason behind the disparity isn’t known. However, researchers believe it likely has to do with differences between genes and hormones.
Typically, females inherit two X chromosomes, while males inherit an X and a Y chromosome. Because of that, all cells in a female’s body go through a process called X chromosome inactivation, which occurs to prevent harmful effects of producing double the amount of X-linked genes.
Some genes manage to escape this process, however, and research suggests they are linked to diseases like lupus. This might explain why lupus affects more women than men.
Migraines
Migraines are the most common form of debilitating headaches that prompt people to see their doctor. They can also cause sensitivity to light and sound, as well as vomiting or nausea. A migraine can last anywhere from a few hours up to two days.
And 3 out of 4 of those affected are women. Women also tend to report more painful and longer-lasting symptoms.
It’s not understood why women are more likely to deal with migraines; however, there is a notable link to hormones. Migraines become more likely once menstruation begins, after giving birth and during perimenopause.
Drops in estrogen levels could play an important role, as 70% of women with migraines report a connection between migraine attacks and their menstrual cycles, according to the Mayo Clinic.
Anxiety
Anxiety disorders are the most common mental disorders in the U.S., affecting up to 40 million American adults annually. Women are more than twice as likely to develop an anxiety disorder at some point in their lives. They also tend to develop anxiety earlier in life than men.
According to the Anxiety and Depression Association of America (ADAA), this is due in part to brain chemistry.
The fight-or-flight system of the brain is more likely to be activated in women, and it remains active longer than in men. That’s partly because of the hormones estrogen and progesterone.
Additionally, the neurotransmitter serotonin plays a key role in a number of brain functions, like responding to stress and anxiety. The ADAA says female brains may not process serotonin as quickly as male brains.
Women may also be more sensitive to low levels of another hormone involved in stress responses, called corticotropin-releasing factor, making them more vulnerable to stress-related disorders than men.
Osteoporosis
Osteoporosis is a disease that causes bones to become weak and easily break. Of the approximately 10 million Americans with osteoporosis, 80% are women.
The Bone Health and Osteoporosis Foundation provides a couple of reasons as to why osteoporosis is more common in women. The first is that women typically have smaller and thinner bones than men to begin with.
Second is that estrogen is an important hormone for protecting bones. In menopause, estrogen levels dip. That can lead to bone loss and osteoporosis.
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