Autoimmune diseases affect about 8% of the population,15 but women are three times more likely to develop one, making up about 80% of those affected.16 We don’t fully know why, but researchers think it might be down to women being the child-bearing sex: the theory is that females ‘evolved a particularly fast and strong immune response to protect developing fetuses and newborn babies’,17 meaning that sometimes it overreacts and attacks the body.18 The immune system is also thought to be behind sex-specific responses to vaccines: women develop higher antibody responses and have more frequent and severe adverse reactions to vaccines,19 and a 2014 paper proposed developing male and female versions of influenza vaccines.20
Sex differences appear even in our cells: in blood-serum biomarkers for autism;21 in proteins;22 in immune cells used to convey pain signals;23 in how cells die following a stroke.24 A recent study also found a significant sex difference in the ‘expression of a gene found to be important for drug metabolism’.25 Sex differences in the presentation and outcome of Parkinson’s disease, stroke and brain ischaemia (insufficient blood flow to the brain) have also been tracked all the way to our cells,26 and there is growing evidence of a sex difference in the ageing of the blood vessels, ‘with inevitable implications for health problems, examination and treatment’.27 In a 2013 Nature article, Dr Elizabeth Pollitzer points to research showing that male and female mice cells have been found to respond differently to stress; that male and female human cells ‘exhibit wildly different concentrations of many metabolites’; and to ‘mounting evidence’ that ‘cells differ according to sex irrespective of their history of exposure to sex hormones’.28
There are still vast medical gender data gaps to be filled in, but the past twenty years have demonstrably proven that women are not just smaller men: male and female bodies differ down to a cellular level. So why aren’t we teaching this?
The inclusion of sex-specific information in textbooks is dependent on the availability of sex-specific data, but because women have largely been excluded from medical research this data is severely lacking. Even the very basics of sex determination have a sex data gap: since the landmark 1990 paper that identified the Y chromosome as ‘the’ sex-determining region, the female sex has – the irony – been seen as the default. But in this case, the default didn’t mean we focused on the female. Rather, research instead focused on testes development as the supposedly ‘active’ process, while female sexual development was seen as a passive process – until 2010, when we finally started researching the active process of ovarian determination.29
Most early research into cardiovascular disease was conducted on men, and women continue to be under-represented, making up only 25% of participants across thirty-one landmark trials for congestive heart failure between 1987 and 2012.30 Women represent 55% of HIV-positive adults in the developing world,31 and in parts of Africa and the Caribbean women aged five to twenty-four are up to six times more likely to be HIV-positive than young men of the same age.32 We also know that women experience different clinical symptoms and complications due to HIV, and yet a 2016 review of the inclusion of women in US HIV research found that women made up only 19.2% of participants in antiretroviral studies, 38.1% in vaccination studies and 11.1% in studies to find a cure.33
Because of their routine exclusion from clinical trials we lack solid data on how to treat pregnant women for pretty much anything. We may not know how a disease will take hold or what the likely outcome may be, although the WHO warns that many diseases can have ‘particularly serious consequences for pregnant women, or can harm the foetus’.34 Some strains of influenza virus (including the 2009 H1N1 swine flu virus) have ‘particularly severe symptoms during pregnancy’. There is also evidence that SARS can be more severe during pregnancy. It is of course understandable that a pregnant woman may be reluctant to take part in medical research, but this doesn’t mean that we have to just throw our hands up in the air and accept that we know nothing: we should be routinely and systematically tracking, recording and collating pregnant-women’s health outcomes. But we aren’t – not even during pandemics: during the 2002-4 SARS outbreak in China, pregnant-women’s health outcomes were not systemically tracked and ‘consequently’, the WHO points out, ‘it was not possible to fully characterize the course and outcome of SARS during pregnancy’.35 Another gender data gap that could have been so easily avoided, and information that will be lacking for when the next pandemic hits.
Like the failure to include women in anatomy textbooks, the failure to include women in medical trials is a historical problem that has its roots in seeing the male body as the default human body, but this traditional bias was radically enhanced in the 1970s, to the great detriment of women’s health, following one of the biggest medical scandals of the twentieth century.36
In 1960 doctors began prescribing thalidomide to pregnant women who suffered from morning sickness. The drug, which had been available as a mild over-the-counter sedative in many countries since the late 1950s, was considered safe because its developers ‘could not find a dose high enough to kill a rat’.37 But while it didn’t kill rats, it did affect foetal development (something that in fact the manufacturers knew as early as 1959).38 Before the drug was taken off the market in 1962, over 10,000 children had been born around the world with thalidomide-related disabilities.39 In the wake
