Inferior: How Science Got Women Wrong – and the New Research That’s Rewriting The Story. Angela Saini

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СКАЧАТЬ female immune system if you’re fighting off infection of any kind, but on the other hand, we are more susceptible to autoimmune diseases, which are very problematic.’

      This isn’t to say that autoimmune disease is always hardest on women. When men get multiple sclerosis, they tend to get it worse. Women also survive with it longer than men do. Even so, of the roughly 8 per cent of Americans who suffer from auto-immune diseases, estimates suggest that at least three-quarters are women.

      ‘In autoimmune diseases, they almost all tend to get worse right before the menstrual cycle in women who are premenopausal,’ says Sabine Oertelt-Prigione. In the same way that varying hormone levels may boost a woman’s immunity at different times of the month, there are theories that they might also affect her experience of illness. There are reports, for instance, that women with asthma are at highest risk of an attack just before or at the start of their period. As oestrogen and progesterone levels drop in the years following the start of the menopause, a woman’s immunity advantage starts to drop away as well.

      When it comes to viral infections, too, a woman’s strong immune response may be a problem as well as a benefit. Research on influenza by Sabra Klein, an immunologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, has shown that while women are generally hit by fewer viruses during an infection, they tend to suffer more severe flu symptoms than men do. She reasons that this may be because women’s immune systems mount sturdier counter-attacks against viruses, but then suffer when the effects of these counter-attacks impact their own bodies.

      Women also tend to get more painful joint and muscle diseases, observes Steven Austad. Part of this is down to autoimmune diseases that affect the joints, such as arthritis. The physical toll of childbearing and the hormonal changes of menopause may also leave women with physical problems and disabilities, especially in later life. Bone density is known to fall short-term after pregnancy, and after the menopause. Weight gain is now also recognised as a symptom of menopause.

      But the overall picture of pain and ill-health is complicated. ‘Cross-culturally, women just report more physical limitations and more disabilities. It’s really widespread,’ says Austad. When it comes to biological clues about the underlying reasons for this sex difference in disease or survival, however, he adds, ‘I don’t feel very confident of any explanation.’

      It’s difficult to tear apart biology from other effects. Society and the environment can sometimes impact illness more than a person’s underlying biology. ‘Women are less likely to go to the hospital when they’re feeling chest pain than men,’ says Kathryn Sandberg, who has looked at gender differences in heart disease in particular. There are countless other ways in which men’s and women’s health habits differ throughout the world. Sabine Oertelt-Prigione points out that where families eat collectively and food is scarce, women are sometimes the last to eat and are the most likely to go without food, which can raise their risk of malnutrition. This in turn can affect their susceptibility to disease.

      Not only a woman’s own behaviour, but that of others around her, can affect her health. From the second a girl is born, she’s placed in a different box from a boy. She may be handled differently, fed differently and treated differently. And this marks the beginning of a lifetime of differences in the way doctors and medical researchers approach her as well. Only very recently, for instance, have doctors begun to acknowledge the severity of some women’s experience of period pain. In 2016, professor of reproductive health at University College London, John Guillebaud, told a reporter that period pain can be ‘almost as bad as having a heart attack’, and admitted that it hasn’t been given the attention it deserves, partly because men don’t suffer from it. In 2015, a team of British researchers studying cancer diagnosis in the UK found that it took longer for women to be diagnosed after going to a doctor in six of the cancers that affect both men and women, including bladder and lung. For gastric cancer, a woman waited on average a full two weeks longer for a diagnosis.

      If there are underlying biological sex differences in health, and the differences aren’t largely down to society and culture, then scientists need to go deeper inside the body to find them.

      ‘Females get sicker but males die quicker,’ says Arthur Arnold, a professor at the University of California, Los Angeles. It’s an old adage, bandied among his undergraduates. It reflects what doctors all over the world have observed, and Arnold is convinced that it reveals the long roots of sex differences in health. He runs a laboratory studying the biological factors that make females different from males, and edits the journal Biology of Sex Differences. His work has taken him beyond looking at organs and sex hormones, and down to the fundamental level of the gene.

      The human body is made up of trillions of cells. Every one of them has genetic information stored in packages known as chromosomes, explaining to our bodies how to build themselves up from the subtlest hormones all the way up to skin and bone. We have forty-six chromosomes in total, split into twenty-three pairs, and the roots of the genetic differences between men and women lie in our twenty-third pair, known as the sex chromosomes. In women, they’re called XX, with one X chromosome inherited from each parent. Men’s sex chromosomes are called XY, with the X coming from the mother and the Y from the father. For a long time it was assumed that these sex chromosomes were mainly concerned with reproduction and not much else. Today some scientists, including Arnold, believe that the consequences of this seemingly tiny genetic difference may stretch much further.

      Every chromosome in a pair carries the same genes in the same locations, known as alleles. The one for eye colour from a person’s father, for example, will be matched by another one for eye colour in the same place from the mother. That’s true of a female’s two X chromosomes too. For males with XY sex chromosomes, however, a matching allele isn’t always there. X and Y don’t have the same genes in the same locations. In fact, the Y is far smaller than the X.

      Having just one copy of the genes on the X chromosome can have repercussions for a man’s body. ‘It’s long been thought, and there is good evidence for this, that having two versions of the gene buffers women against certain diseases or environmental changes,’ says Arnold. If a man happens to have a genetic mutation on one of his X chromosomes that causes an illness or disability, he has no way of avoiding it. A woman, on the other hand, will have an extra X chromosome to counteract it, unless she’s unlucky enough to have the same genetic mutation on both of her X chromosomes, one from each parent. ‘The simple case would be if one gene works better when it’s cold and another works better when it’s hot. A woman with both of those alleles can be healthy when it’s hot and cold. The male only gets one shot. He only has one copy. So his body either works better when it’s hot or works better when it’s cold, but not both.’

      There are some well-known genetic traits to which men are more susceptible than women simply because they have one X chromosome. These X-linked disorders include red-green colour blindness, haemophilia, muscular dystrophy and IPEX syndrome, which affects immune function. Mental retardation, which affects 2 to 3 per cent of people in developed countries, and significantly more men than women, also has a strong link to the X chromosome.

      This is a reason why, in the effort to understand sex differences in health, Arthur Arnold has chosen to zero in on chromosomes. ‘We went back to the most fundamental biological differences between males and females. From the time of the fertilisation of the egg, the only one thing that we know is different between males and females is sex chromosomes. So everything has got to come from that … everything’s downstream of the sex chromosomes.’

      ‘What we know of X-linked diseases is that they’re pretty rare,’ says Steven Austad. ‘But I think there are a lot more X-linked diseases than we think about. I think this probably underlies a considerable proportion of the sex difference.’ One example is respiratory syncytial virus, which infects the lungs and breathing passages and is one of the biggest causes of bronchitis in children under the age of one in Britain СКАЧАТЬ