Wintertime always brings up the question of vitamin D supplementation. In my last year of medical school, I was seeing patients in a resident-run clinic where a patient sheepishly asked the resident I was following if she could have her vitamin D level checked. My resident quickly waved his hand and dismissed her request saying “No, we don’t check those. Everyone is low and so we don’t treat it.” It took all my willpower to bite my tongue and not say anything. Not only was her request warranted, but his response was downright insulting!
What is Vitamin D? Vitamin D is actually a group of 5 different prohormones, with vitamin D2 (derived from plants and fortified in foods like cereal) and vitamin D3 (derived from UVB rays hitting our skin and animal-based foods like fatty fish), being the most notable. Although people say, “I get plenty of sun in the summer, so I only supplement in the winter,” I wouldn’t assume they are vitamin D sufficient. In fact, it is thought that, even on exposed skin, little vitamin D3 is made at latitudes about 37 degrees north or below 37 degrees south of the equator. My home state of Minnesota is at roughly 45 degrees north of the equator, so good luck to even the most devoted of sunworshippers. (Plus, who wants to sunbathe all day when we have skin cancer to worry about?) Not only is vitamin D good for bone health, but newer research is linking low vitamin with increased risk of multiple health conditions. In fact, you can Google “Vitamin D and (blank)” and you will get oodles of research papers and opinion pieces on their associations. I could write for days on vitamin D’s influence on numerous health conditions, but I picked a few I felt were worth noting. *Make note though, and there are inconsistencies between studies, and more research is needed to better characterize and solidify associations and mechanisms of action.
Low Vitamin D Low vitamin D has been linked to a variety of mental health conditions, including depression, attention deficit hyperactivity disorder, and bipolar disorder, to name a few. Science is still learning the mechanism, but one possible reason is that vitamin D is needed to activate the enzyme tryptophan hydroxylase 2, which is needed to synthesize serotonin (the happy, calming, post-thanksgiving turkey, neurotransmitter). Lower vitamin D has also been linked to suboptimal fertility in both women and men. Gonadal tissues of both sexes have vitamin D receptors, and low vitamin D has been associated with histologic changes in the gonadal tissues, as well as decreased sperm count and motility, and can influence clinical pregnancy rates in IVF.
Importance of Vitamin D Vitamin D has been getting a lot of attention in the medical world for its immunomodulatory abilities. Vitamin D can help stimulate the innate (first-line defense) immune system, as well as stimulate T-regulatory cells (help turn down the immune system when no longer needed and prevent autoimmune attack). As such, low vitamin D has been linked to increased risk of acute respiratory illnesses, as well as associations with autoimmune disease and cancers. There are numerous other health conditions that effected by vitamin D status, including cardiovascular disease risk, diabetes (both Type 1 and Type 2), and pain. However, I think you get the hint that adequate vitamin D level is good for health. So, what is an adequate level? That has been, and still is, hotly debated. Most medical societies can agree that a vitamin D level of 30ng/ml is adequate for bone mineral density and dental health. However, these are easier to study (it is pretty easy to compare how many people meet the criteria for osteoporosis, or how many people with osteoporosis sustain a fracture). But when it comes to conditions like “cardiovascular risk” and “immune function”, the waters are murky. After reading a few papers, it looks like vitamin D levels slightly higher than the 30ng/ml may be better for other health conditions. Vitamin D level of 40ng/ml-70ng/ml are likely optimal for general health. Some rheumatologists and integrative medicine providers will push vitamin D to the upper end of normal for their autoimmune disease patients. I would not recommend going much higher than 70ng/ml, especially without frequent monitoring, as vitamin D toxicity can cause hypercalcemia, which can cause a variety of dangerous neurologic, gastrointestinal, and cardiac side effects. Most people can get to sufficient vitamin D levels with a supplementation of 1,000-2,000 IU daily, but requirements vary depending on absorption and fat distribution. Thus, if you are currently supplementing without medical oversight, I would recommend starting at 2,000 IU daily of vitamin D3, but make sure to have your level tested at least once within 3-6 months, so that you can adjust as needed.