The modern environment, including diet and stress, may be driving the surge in autoimmune conditions. Photo / 123rf
Autoimmune diseases are rising worldwide, and it’s not purely explained by genetics.
Autoimmune diseases are rising worldwide, and it’s not solely explained by genetics.
Autoimmune diseases are conditions that occur when the immune system attacks the body.
There are more than 100 conditions considered autoimmune, including better-known ones such as rheumatoid arthritis, lupus and multiple sclerosis, as well as the lesser-known ones such as scleroderma and autoimmune hepatitis.
In the United States, 20% of 1 in 5 Americans has an autoimmune condition. [According to the Australasian Society of Clinical Immunology and Allergy, they affect around 5% of people and are one of the most significant chronic health problems in Australia and New Zealand.] They affect women more than men, and they often run in families, though genetics is just one risk factor for these diseases. Autoimmune conditions are increasing in a way that isn’t accounted for by our genes alone - for instance, between 1950 and 2000, the incidence rates of Crohn’s disease, multiple sclerosis and Type I diabetes rose by 300% or more.
And if we dive deeper into what’s changing, the story becomes more complex. Not only are autoimmune diseases rising, but they’re often occurring at a younger age. Earlier-onset autoimmune diseases pose unique challenges - a chronic illness that begins in childhood can seriously alter the individual’s and their family’s lives. And early-onset disease can increase the risk of developing other autoimmune conditions.
Furthermore, autoimmune diseases are rising where they were once less common. A well-studied example is inflammatory bowel disease, which through most of the 20th century was vastly more common in North America and Europe, but in recent decades has been increasing in South America, Asia and Africa.
And we’re seeing an intriguing pattern in many autoimmune diseases: When people move to other countries, their children’s disease risk resembles that of the local population - not that of their parents’ country of birth. For example, the incidence of Type I diabetes in Pakistan is about 1 case per 100,000 people, while in the UK, it’s more than 10 times higher. But the rate of development of Type I diabetes among the children of Pakistani people who have moved to the UK mirrors that of the general UK population.
An older theory about the origin of autoimmune and allergic diseases is called “hygiene theory,” which said that too much cleanliness - or, more specifically, a decline in infectious diseases and rise in antibiotic use - has weakened our immune systems.
Our environment, which interplays closely with our genome, probably is a big part of this story. However, it’s become clear that hygiene theory doesn’t quite capture what’s happening: Our risk of these diseases appears to be more tied to our exposure to day-to-day microbes, as opposed to true infectious pathogens. This includes the microbes we encounter via the birth canal as babies, those in our gut (in turn largely influenced by diet), and interactions with other children such as in daycare, as well as animals at home or in farms.
And while some aspects of our modern environment are “cleaner” today than in the past, unhealthy changes that increase our risk of autoimmune diseases are pervasive: Our food is increasingly ultra-processed, we’re constantly stressed and sleeping poorly, and air pollution is rampant in much of the globe. All of these factors have been shown to play a role in developing autoimmune conditions (so simply minimizing your personal “hygiene,” such as avoiding washing hands, is probably not a helpful way to mitigate risk).
And there’s another piece of the puzzle. More young people are being diagnosed with cancer. These two phenomena - cancer and autoimmune disease - are the yin and yang of immunology. Our body’s immune system is constantly hunting for and eliminating cancers in our bodies. Many environmental risk factors that may help those cancers evade detection today are different from those of generations past - and are hitting us at younger ages. For instance, our increasingly sedentary lifestyles, the consumption of sugary beverages and the obesity epidemic that was particularly impactful to children during the pandemic. In turn, as our immune system becomes increasingly primed by more and more perceived dangers, it can mistakenly turn against itself.
And just as cancer risk rises with age, so do to antibodies targeted against ourselves - adults aged 50 or older tend to have a higher prevalence of these antibodies than people in their 20s through 40s. But even more concerningly, those antibodies have become more common in recent decades: About 15% of people 50 and older had one such antibody, known as an anti-nuclear antibody, in their blood between 1988 and 1991. When a comparable group was checked between 2011 and 2012, that number had risen to over 20%.
We’re just starting to learn how these antibodies may affect multiple aspects of our health. Patients with a variety of known autoimmune conditions frequently have severe gut symptoms that we do not yet fully understand. A subset of these patients also have joint hypermobility and issues with blood pressure and heart rate, such as Pots, which scientists hypothesise may all share an immunological basis.
As shown by these factors - some of which we have far less control over than others - autoimmune diseases aren’t necessarily preventable. But steps that may reduce the risk such as eating whole foods and mitigating stress are always worth taking, especially if, for example, there is a strong history of autoimmune diseases in your family.
A large study of more than a million Danish women found pregnancy was associated with a 15% increased risk of autoimmune diseases after a vaginal delivery, and a 30% increased risk after a C-section delivery, but there are many unanswered questions. We know that women, regardless of pregnancy, experience greater rates of autoimmune diseases than men. A major cell study earlier this year identified a molecule expressed only in women that inactivates their second X chromosome, thought to be a possible culprit.
One hypothesis specific to pregnancy involves fetal microchimerism. The term refers to the phenomenon in which, as a baby grows in the mother’s uterus, small amounts of fetal cells are released into the mother’s bloodstream and may exist in the mother’s body for years afterward. Some, but not all, studies support a link between fetal microchimerism and autoimmune disease. Scientists are still working to better elucidate these possible pathways.
Many of my patients have asked about the link between the coronavirus and autoimmune diseases.
SARS-CoV-2 infection can cause major immune malfunction - few of us who treated these patients in 2020 will forget the cytokine storms, a rapid and life-threatening surge of inflammation driven by the immune system, that affected many of those who died. But for many Covid survivors, changes in the immune system possibly triggered by the virus appear to remain altered long after the acute infection is over.
How much of the broader set of symptoms falling under long Covid have an autoimmune origin is not totally clear. We do know that in a 2023 study of more than 1 million Covid patients in Hong Kong, there was a significantly increased risk of later being diagnosed with autoimmune conditions such as rheumatoid arthritis and psoriasis compared with those who were not infected. Among Covid patients, the study also found that completing two doses of a coronavirus vaccine mitigated that risk. Several other viruses such as the Epstein-Barr virus and herpes simplex virus have similarly been found to increase the risk of autoimmune conditions.
I advise my patients to take precautions against the coronavirus, such as masking and vaccines, because researchers are still investigating the long-term consequences of Covid, including the risk of being diagnosed with an autoimmune condition.
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