Vitamin D - The 5 most common questions asked by patients. Are you getting enough vitamin D this summer?

1. Can we make enough vitamin D from the sun?

Only three known sources of vitamin D exist; sunlight, diet, and vitamin D supplements. The major source of vitamin D is our exposure to natural sunlight.

Various factors are needed in order to make adequate vitamin D from the sun. The first is what is known as the “shadow” test - if a person’s shadow is taller than the length of the their body, he/she isn’t producing vitamin D at that time of day. This is because UVB rays, which promote the activation of vitamin D in our bodies, can only do so when they penetrate the atmosphere at an angle between 45 and 90 degrees. 

Geography, season, and ultraviolet (UV) index are other important factors that determine whether vitamin D can be synthesized. The UV index, which is highest between 10am and 4pm as well as in the summer months, typically must be above 3 in order to make any vitamin D. Other than during the summer months, the skin makes little/no vitamin D at latitudes above 37 degrees (keep in mind Ontario is located above 37 degrees north!).

As well, since a darker skin tone is a natural sun protector, these individuals require at least three-to-five times longer sun exposure to make an equivalent level of vitamin D as someone with a fair/light skin tone!

The amount of skin exposed to the sun also matters. Generally, the greater the surface area exposed, the more vitamin D is produced. To put this into perspective, one study showed that full body exposure of a fair-skinned individual to 10-15 minutes of midday summer sun resulted in the synthesis of approximately 15,000 IU/day of vitamin D3.

2. Does sunscreen reduce vitamin D absorption?

There is some controversy surrounding this topic. Some research has found that wearing a sunscreen of SPF-30 reduces vitamin D synthesis in the skin by more than 95%. So, it is possible that wearing sunscreen may inhibit some conversion of sunlight to vitamin D.

3. What is the clinical importance of testing vitamin D levels?

The role of vitamin D goes beyond the regulation of calcium and bone health. We know that low vitamin D levels are associated with common chronic disease, including autoimmune diseases, diabetes, and neuropsychiatric disorders. 

Recent literature in the Journal of National Cancer Institute looked at pooled data consisting of 5,706 participants with colorectal cancer and 7,107 people without colorectal cancer. It found that vitamin D is inversely associated with colorectal cancer risk - that is, lower vitamin D levels were associated with a higher risk for colorectal cancer. In fact, vitamin D levels below 12 ng/mL was associated with a 31% increased colorectal cancer risk!

Testing is also important because it can identify whether someone’s levels are too high. While this does not occur often, “toxic” levels of vitamin D can lead to harm, including causing high calcium levels in the blood, heartbeat irregularities, and kidney damage.

4. What is the best form for supplementation - liquid, tablet, or chewable? 

It’s more important that vitamin D be taken with food, which can increase its absorption by 30-50%. Liquid (drops) are usually in an emulsified form, meaning that they are already blended with fat, so they are by default in a highly absorbable form. Vitamin D supplements are available in two distinct forms, ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D3 seems to be more effective at raising serum vitamin D (25-hydroxyvitamin D) levels than vitamin D2.

5. Can we get vitamin D from food only?

Surprisingly, there aren’t many foods high in vitamin D. Fatty fish, such as salmon and tuna, cod liver oil, and some dairy products are examples of foods that are high in vitamin D. But the list mostly ends there!

 Did you know that as primary care providers, naturopathic doctors in Ontario can requisition blood work to test for vitamin D levels? As always, it is important to work with a health professional regarding matters of your health. 

Dr. Dominique Vanier is a registered naturopath in Burlington with a clinical focus on digestion and women’s hormones. Naturopath Burlington. This article is for information purposes only. It is not intended to treat or diagnose any health conditions.

References

1. McCullough, M., Zoltick, E., Weinstein, S., Fedirko, V., Wang, M., & Cook, N. et al. (2018). Circulating Vitamin D and Colorectal Cancer Risk: An International Pooling Project of 17 Cohorts. JNCI: Journal Of The National Cancer Institute. doi: 10.1093/jnci/djy087

2. Mostafa, W., & Hegazy, R. (2015). Vitamin D and the skin: Focus on a complex relationship: A review. Journal Of Advanced Research, 6(6), 793-804. doi: 10.1016/j.jare.2014.01.011

3. Vanchinathan, V., & Lim, H. (2012). A Dermatologist's Perspective on Vitamin D. Mayo Clinic Proceedings, 87(4), 372-380. doi: 10.1016/j.mayocp.2011.12.010

4. Wang, H., Chen, W., Li, D., Yin, X., Zhang, X., Olsen, N., & Zheng, S. (2017). Vitamin D and Chronic Diseases. Aging And Disease, 8(3), 346. doi: 10.14336/ad.2016.1021