Type I diabetes has been on the rise since the middle of the 20th century. From 1990 to 1999, the incidence increased by 3% per year.
Unlike type II diabetes (T2D), which is a relative insulin deficiency (where the body can’t keep up with the body’s demands), type I diabetes (T1D) is an absolute insulin deficiency, where the body can’t produce enough insulin because of autoimmune destruction of beta cells which produce insulin.
T1D is an autoimmune disease, and like most autoimmune diseases, researchers are still scrambling to figure out what’s going on in T1D and how to prevent it. This is once again in contrast to T2D, where there are known modifiable lifestyle risk factors, like eating habits and how active you are.
While many here know that there is some research on the link between vitamin D and T1D, and some researchers think vitamin D deficiency may contribute to the rise in incidence of T1D, there are actually a few different hypotheses why there is a rise in T1D incidence. In a recent review, Dr Francesco Egro took a look at all the hypotheses.
Here they are:
- Hygiene hypothesis. This is the theory that exposure to infectious agents in early childhood protect against T1D. Since the incidence of infections like tuberculosis, measles and mumps have gone down, T1D incidence has gone up. This hypothesis has gained some merit through animal models. There are some proposed mechanisms, too, how lack of exposure would cause T1D.
- Viral hypothesis. This is the theory that viruses like enterovirus, rubella virus, mumps virus, rotavirus and cytomegalovirus accelerate the autoimmunity of T1D. Like the hygiene hypothesis, this theory has proposed mechanisms. However, unlike the hygiene hypothesis, this theory does not explain the rise in incidence the last 50 years.
- Vitamin D deficiency hypothesis. This is the theory that vitamin D deficiency either causes T1D or contributes to the incidence. This idea is supported by the fact that the first T1D autoantibodies usually appear in the fall or winter, when vitamin D levels are lowest. A Finnish cohort study also found that babies who received 2000 IU of vitamin D/day during infancy were less likely to develop T1D later in life compared to children that didn’t get that much. Vitamin D plays a hand in the immune system, although the mechanism by which vitamin D deficiency would cause T1D has not been proposed.
- Breast-feeding vs cow’s milk hypotheses. This is the theory that insufficiency in breastfeeding of genetically susceptible children may lead to T1D. A few studies have shown that there is a protective association against T1D in breastfeeding. There are some proposed mechanisms how cow’s milk and/or lack of human milk would cause T1D. The decrease in breastfeeding over the years could also explain the increase in incidence.
As you might have noticed, all of these theories have some overlap and similarities. They all involve some aspects of the immune system, and they all have both a protective element to them and a diabetogenic element to them (diabetogenic meaning causing T1D).
Could the incidence and increase in T1D be a combination of all of these hypotheses? If we took this idea and turned it into a model, it would look like this:
While it’s hard to know what exactly is going on in T1D with still much research needed, all the vast and different areas of interest in T1D likely make it a disease with multiple factors, vitamin D playing just one part.
But that doesn’t diminish the importance of vitamin D in T1D, if it’s indeed implicated. Researchers believe the body may have a compensatory system at play, where for instance if one doesn’t get enough human milk during infancy, they can make up for it by getting enough vitamin D.
Likewise, the opposite holds true, too. Theoretically speaking, if one doesn’t get enough vitamin D during infancy, they can make up for it by getting breastfed, at least in the case of T1D (again, in theory). This is why, as in all diseases that vitamin D may play a role in, not getting enough doesn’t necessarily mean you’ll develop particular diseases. But coupled with a few other factors, vitamin D deficiency could be the final trigger in disease onset. That is why making sure you get enough vitamin D is so important and could have a huge impact in making a healthier human population.