Today, we’re happy to welcome D-Mom and fellow type 1 Sarah Howard in upstate New York sharing some important new research. Sarah’s no stranger to the online community, as she writes at the Diabetes and Environment site and works with The Collaborative on Health and the Environment non-profit group, focusing on environmental factors that impact public health.

Sarah’s been exploring some of the latest research on Vitamin D — you know, that important calcium-providing nutrient often associated with exposure to sunshine and found in very few foods, like the fleshy parts of fish. Research to date has been sketchy on just how Vit. D connects to and possibly even plays a part in the onset of diabetes, but Sarah’s got the update on the latest findings. Here’s what she’s found, and how it circles back to her own family’s life with diabetes (and possibly yours, too!).

I have type 1 diabetes, and so does one of my two boys. Why? I have no idea.

We still don’t know what causes type 1 diabetes, but we do know that the children of parents with type 1 have a higher risk of developing it—about 10 times higher than the general population. The numbers vary depending on where you look, but at the high end (in Finland), a child whose parent has type 1 has about a 7% chance of developing it by age 20.

So what can a parent do to reduce that risk? Well, the bad news is that we still don’t know — that is, there have been no double-blind randomized controlled intervention trials that have successfully reduced the risk of developing type 1 diabetes.

But the good news is that a large international study has just been published that found that higher Vitamin D levels during infancy and childhood are associated with a lower risk of developing type 1 diabetes-related autoimmunity in children, especially in children with certain genes.

Back when I was pregnant, I had assumed that because I was outside a lot, my Vitamin D levels would be fine. They weren’t. I wish I had known about this before one of my children got diabetes.

The study states, “Although ours is an observational study, our results suggest that attaining Vitamin D sufficiency in children at risk for developing type 1 diabetes may have a protective role.”

Over many years of reading scientific literature on type 1 diabetes, this is the closest I’ve seen to a recommendation of a way to *possibly* reduce the risk of type 1 diabetes, or at least autoimmunity, which is of course strongly linked to the eventual development of type 1 diabetes.

It’s not quite a full recommendation — the authors would need a successful intervention trial to state that — but in the meantime, anyone can ask their doctor to check their child’s Vitamin D levels, to make sure they are high enough.

So what is high enough?

The U.S. Institute of Medicine (IOM) suggests that 25(OH)D concentrations of at least 50 nmol/L are sufficient, so that’s the number that these authors used to define “sufficiency.” (Technically, they defined sufficiency as an average plasma 25(OH)D concentration over all time points of ≥ 50 nmol/L, starting at age 3-12 months, and averaged from there over childhood).

This study, by the way, is based on data from the TEDDY (The Environmental Determinants of Diabetes in the Young) study, which includes six study centers in the U.S. and Europe.

Among these TEDDY children, using their definition of sufficiency, Vitamin D levels were sufficient in 58% of them during childhood, and in 49% of them during infancy. Of the 42% that were insufficient (below 50 nmol/L) during childhood, 6% were low enough to be considered Vitamin D deficient, that is, their average childhood Vitamin D levels were below 30 nmol/L (thus there were not enough children to analyze the association between true Vitamin D deficiency and islet autoimmunity).

On the other end of the spectrum, high levels of Vitamin D – more than what the IOM defines as sufficient – did not seem to make much difference. Some organizations, including the Endocrine Society, recommend Vitamin D levels over 75 nmol/L, but in this study, the association was consistent in people at any level over 50 nmol/L, as compared to under 50 nmol/L. Good to know.

By the way, since only 10% of the children had levels over 75 nmol/L, which the Endocrine Society considers sufficient, and fully 42% were insufficient by the IOM definition, there is a lot of room for improvement here. The recommended dosages of Vitamin D vary by age, weight, medications taken, etc., so please ask your doctor before supplementing.

Based on all the research, here are some handy tips relating to Vitamin D and diabetes:

Watch your units!

Your 7th grade math teacher was right; always double check your units. I checked my recent lab report, and at first my number looked pretty low. But then I noticed that my Vitamin D levels were given in ng/ml, not nmol/L. I converted my numbers to mmol/L using this online conversion tool, and it’s great. An IOM sufficient level of 50 mmol/L works out to 20 ng/ml, and an Endocrine Society sufficient level of 75 mmol/L translates to 30 ng/ml, so since my level of 39 ng/ml is about 97 mmol/L, it is in fact pretty high. But it is only high because I take Vitamin D supplements, and I take those because I used to be Vitamin D deficient — back when I was pregnant and nursing, which no one recommends!

Does timing matter?

This study looked at Vitamin D levels in early infancy, defined as 3-12 months of age, and also throughout childhood. Overall, higher Vitamin D levels during both infancy and childhood were associated with lower autoimmunity risk. Just considering levels during infancy alone, Vitamin D sufficiency was associated with a 40% lower risk of autoimmunity, as compared to insufficiency. Considering childhood levels alone, Vitamin D sufficiency was associated with a 31% lower risk.

Does location matter?

No. The association between Vitamin D levels and autoimmunity did not differ for children in Finland vs Seattle, for example, or among any other study centers.

Single vs multiple antibodies

Testing positive for a single autoantibody is associated with a higher risk of developing type 1 diabetes, and testing positive for more than one antibody provides an even greater risk. When looking at single versus multiple antibodies, this study found similar results for both.

Note that this study has not followed children long enough (yet) to determine whether Vitamin D levels reduce the risk of developing full-fledged type 1 diabetes, after developing autoimmunity. According to Dr. Jill Norris, the lead author, they are now working to answer that question.

What is up with the genes?

While numerous past studies have found that lower Vitamin D levels or intake were associated with a higher risk of type 1 diabetes, many others have not found an association. The authors of this study suggest that perhaps the differing results are because the earlier studies generally did not consider genetic background in their analysis. Also, the past studies were smaller, and did not necessarily follow people over time (especially beginning in infancy).

In some children, those without certain gene variants, Vitamin D levels were not related to autoimmunity. In children with one gene variant, there was an association. In children with two gene variants, the association was even stronger. And so on. That means for some people, Vitamin D levels may not matter much (for autoimmunity anyway, they might matter for other health issues like bone health or colon cancer). For others, Vitamin D levels may matter a lot. But without genetic testing, we don’t know who falls into which group.

It’s complicated… (?)

Those who know way more than I do about this stuff can tell you that it’s even more complicated—for example, these authors measured 25(0H)D levels, not the more active 1,25(OH)2D3 levels. OK fine, but I still think the findings are worth spreading to everyone with a kid at potential genetic risk of type 1 diabetes. It turns out there are a lot of things that can affect Vitamin D levels, in addition to genetic background, such as skin color, age, weight, and, as a few studies are starting to show, even environmental chemical exposures.

Actually it’s not complicated!

It’s pretty simple. Higher Vitamin D levels are associated with a lower risk of type 1 diabetes-related autoimmunity in children. While the association depends on genetic background, we can’t control our DNA, but we can control our Vitamin D levels.

Thanks for reporting on this important research, Sarah! We appreciate your passion and attention to detail.