Diabetes, both types 1 and 2, are potentially life threatening and certainly life changing conditions that affect people worldwide. Case numbers increased nearly fourfold between 1980 and 2014 according to the World Health Organization (WHO), with associated increases in mortality and disability caused by the disease.
The majority of those cases are type 2 diabetes, caused by excess visceral fat, though the interaction between genetic susceptibility, environment, obesity, and sedentary lifestyle is complex. It is not uncommon for people to have a moderate body mass index (BMI) and type 2 diabetes, though they still respond to weight loss.
Case numbers of type 1 diabetes are also growing. The reasons for this are not well understood, but some have compared the increase in type 1 diabetes cases to those of other autoimmune diseases such as multiple sclerosis. Both are more common in the northern hemisphere, as is vitamin D deficiency.
In fact, estimates suggest that as many as 40% of Europeans are vitamin D deficient, and 13% may be severely so — and the situation is worse still for individuals with dark skin. It is also difficult to ascertain how many people are deficient, as debate rages over the definition of deficiency.
Dr. Victoria Salem, a consultant endocrinologist and clinical scientist based at Imperial College London, told Medical News Today in an interview: “We know that type 1 diabetes is much more prevalent in the northern hemisphere and that’s usually put down to the fact that we get less sunlight and therefore have less vitamin D levels. That’s true also for multiple sclerosis. But it’s essential that that’s an association.”
While it is just an association, the links do not stop there. “[There is] quite good data showing that vitamin D deficiency, frank deficiencies — so children who’ve got rickets — are much more likely later in life to develop type 1 diabetes. But equally, people who are given a high dose of vitamin D […] are also less likely to get type 1 later on,” she explained.
Of course, suggesting vitamin D, or lack of it, is responsible for disease or susceptibility to it, is rife with controversy. Particularly with the heavily racialised discussion over the role of vitamin D deficiency in susceptibility to COVID-19.
The controversy over the role of vitamin D in diabetes is most likely due to poorly designed trials that have failed to adequately measure the impact of vitamin D supplementation on groups that can be generalized, a recent update in the European Journal of Clinical Nutrition argued.
Type 2 diabetes is typically diagnosed when high blood glucose levels are detected. This is ultimately caused by low insulin sensitivity in the tissues which makes it hard for the body to take glucose out of the blood.
To compensate for this lack of sensitivity, the body creates a larger amount of insulin until eventually the beta cells in the pancreas give up, and the affected individual cannot produce enough insulin to transport glucose into their cells, resulting in high blood sugar. It is often at this point that people receive the diagnosis of type 2 diabetes.
Dr. James Brown from Aston Research Centre for Healthy Ageing, Aston University in Birmingham, United Kingdom, studies type 2 diabetes and metabolism and explained the theory to MNT in an interview:
“If you look at the basic biology of vitamin D and what happens in diabetes, there is evidence that vitamin D improves what we call insulin sensitivity, which is a key part of type 2 diabetes. And also evidence that vitamin D increases insulin secretion, and those two things are what effectively go wrong in type 2 diabetes as you become insulin resistant and your insulin doesn’t work as well […] So there is, if you like, a theoretical basis for these studies being done.”
Dr. James Brown