This article uses sex (assigned based on anatomy) and gender (associated cultural norms) in reference to women, as both have an influence on medical research and care.

At least since Ancient Greece, the default human body was established as male. Hippocratic physicians thought of the female body as abnormal, and others believed that female bodies were simply male bodies turned inwards due to a deficiency in ‘vital heat’. This trend in thinking continued for the next several thousand years.

Even today, there is a prevailing belief that female bodies differ from male bodies only in size and reproductive organs, with the underlying understanding that men’s biology is the default. The medical stance was summarised by Leonore Tiefer in 1992:

‘Men and women are the same, and they’re all men.’

Indoctrination into this belief within the medical profession starts early. A 2008 analysis of recommended medical textbooks found that three times as many male as female bodies were used to illustrate neutral body parts. The study concluded that in western anatomy textbooks, the white male is presented as the ‘universal model’ for human bodies.

But women do differ from men in more than size and reproductive organs.

Approximately 8% of the population have autoimmune diseases, but women make up about 80% of those affected. The reasons for this are not fully understood, though there is some idea that women have evolved a particularly strong immune response to protect developing foetuses – sometimes it overreacts and attacks the body itself. This could also be a possible explanation behind the results of studies that show sex-specific differences in vaccine outcomes – women develop a stronger antibody response, but also have more frequent and more severe adverse reactions.

But differences in response to medical treatments are largely absent in the scientific literature, making the knowledge of sex-specific vaccine reactions somewhat of a rare gem. The medical sphere is plagued by a ‘gender data gap’, as Caroline Criado Perez describes it in her book Invisible Women: Exposing Data Bias in a World Designed for Men.

Sex-specific knowledge within the medical community is ‘dependent on the availability of sex-specific data,’ she writes, ‘but because women have largely been excluded from medical research, this data is severely lacking.’ And when women are included in medical trials, the researchers often fail to examine the differences between the sexes.

A 2014 report by from the Brigham and Women’s Hospital in Boston summed up the issue:

‘Medical research that is either sex- or gender-neutral or skewed to male physiology puts women at risk for missed opportunities for prevention, incorrect diagnoses, misinformed treatments, sickness, and even death.’

Sildenafil citrate, the active ingredient in Viagra, was discovered as a treatment for erectile dysfunction when it was being tested as a heart medication in the early 1990s. If more women had been included in the original trials, its possible effectiveness as period pain relief would have been discovered before 2013. And if women’s health was given equal consideration as men’s, further funding requests would not have been denied.

One of the starkest examples of male default bias is so prevalent, it has its own name: Yentl Syndrome.

In the film Yentl, Barbra Streisand’s character had to dress up as a man to receive an education, so the name came to refer to the phenomenon that women who have ‘male-pattern’ Coronary Heart Disease are more likely to get the appropriate diagnosis and treatment.

However, most women don’t present with the chest and left arm pains of a ‘Hollywood (male-pattern) Heart attack’. Instead, they have stomach pain, breathlessness, nausea, and no chest pain at all. Because of this, women are 50% more likely than men to be misdiagnosed following a heart attack, which is not a surprise when the patient populations used to study the disease were at least two-thirds male.

This is especially worrying considering CHD is the leading cause of death worldwide. An editorial in the European Heart Journal said that contemporary data demonstrates ‘persistently more adverse outcomes for women compared with men’ – because a higher proportion of women do not have male-pattern presentation, relatively fewer women are treated, so more women die.

The problem with male-default thinking in medical research costs lives. Women need to be included in all levels of research, and sex differences need to be studied, so doctors can provide care which is as informed about women as it is about men.