I love being out in the sun. And not just because I like it, but also because of the abundant evidence linking sunlight exposure with a reduced risk of conditions such as cancer and multiple sclerosis as well as improved physical and psychological functioning. And it’s free. And I like sporting a tan.
I recently wrote about warnings here in the UK about a supposed resurgence in the bone disease ‘rickets’ in children. Until this week, I was unaware that another condition that generally starts in early life that might be caused by a deficiency of vitamin D is type 1 diabetes.
Diabetes is characterised by raised levels of sugar in the bloodstream. It comes in two main forms: type 1 and type 2. About 90 per cent cases are type 2 in form. Here, there are usually normal or even raised levels of insulin in the body. The problem usually is that the insulin doesn’t work very well. As a result, blood sugar levels are not adequately controlled.
Type 1 diabetes is different in that it is caused by inadequate levels of insulin. This condition normally develops in childhood or adolescence. It is believed to be caused by a destruction of the cells in the pancreas that are responsible for making insulin. The destruction of these cells (known as the beta-cells) comes at the hands of the body’s immune system. Type 1 diabetes is sometimes regarded, therefore, as an ‘autoimmune disorder’.
What alerted me this week to the potential link between vitamin D and type 1 diabetes was a study published on-line in the Archives of Disease in Childhood. In this study, researchers pooled together (in the form of what is known as a ‘meta-analysis’) the results from 5 epidemiological studies looking at the relationship between vitamin D supplementation in infancy (up to 1 year of age) and subsequent risk of developing type 1 diabetes.
In short, what was found that vitamin D supplementation was associated with a 29 per cent reduced risk of type 1 diabetes.
Now, epidemiological studies of this nature can’t prove that vitamin D is actually protecting against type 1 diabetes (just because two things are associated, doesn’t mean one is causing the other). However, the researchers found that the relationship between vitamin D supplementation and diabetes risk was ‘dose-dependent’. In other words, generally speaking, the higher the level of vitamin D supplementation, the lower the risk of diabetes. This finding does support the idea that vitamin D has a genuine protective role.
More supporting evidence comes in the form of research which has found that individuals diagnosed with type 1 diabetes tend to have lower levels of vitamin D in their bodies compared to those who do not have this condition.
Also, type 1 diabetes risk has been noted to be higher in countries where sunlight levels are lower (sunlight drives vitamin D production in the skin).
If vitamin D does actually protect against type 1 diabetes, how does it do it?
In this study, reference is made to the fact that vitamin D receptors exist on both the beta-cells in the pancreas that make insulin, as well as some cells in the immune system. It might be that vitamin D may help to ‘normalise’ immune activity (and reduce a tendency to ‘overreact’ to the beta cells and/or helps to protect the beta-cells from damage. Evidence from animal experiments suggests vitamin D has the ability to protect against type 1 diabetes through effects on the immune system.
To know for sure if vitamin D protects against type 1 diabetes would require randomised controlled trials (i.e. trials in which children are treated with vitamin D or placebo). In the absence of these trials, though, my tendency is to take this most recent study as another piece in the ever-growing body of evidence linking vitamin D (and sunlight) with benefits for health and disease-protection in both adults and children.
Zipitis CS, et al. Vitamin D Supplementation in Early Childhood and Risk of Type 1 Diabetes: a Systematic Review and Meta-analysis. Arch Dis Child. [e-pub 13 March 2008] doi:10.1136/adc.2007.128579