By Dr. Rachelle Viinberg, BSc, ND
Vitamin D, once thought to influence little more than bone diseases such as osteoporosis and rickets, is now recognized as a major player in overall human health. In fact, vitamin D is involved in so many physiological functions that, once the benefits are tallied up, it’s easy to wonder if there is anything this fat-soluble vitamin does not do.
So what is Vitamin D exactly? Activated vitamin D is not a vitamin in the usual sense of the word, which is generally a cofactor in an enzymatic reaction or antioxidant. Vitamin D is unique in that it is a seco-steroid hormone. As with all steroid hormones, it acts as a molecular switch to signal genetic transcription (1). In fact, more than 1000 human genes are direct targets of vitamin D, which has an effect on multiple organs including the heart, lungs, adrenal medulla, neurons, muscle, pituitary, bone and brain (2). This is one of the primary reasons why Vitamin D can impact such a wide variety of diseases, including:
|Diabetes 1 and 2
Vitamin D and Athletic Performance
Not surprisingly, Vitamin D can have a strong impact on athletes as well. In fact, the athletic performance enhancing effects of vitamin D have been assumed by the former Soviet Union and its satellite states for decades. In the early 20th century, Russian and German researchers used sunlamps to stimulate vitamin D production in their elite athletes. The increases in athletic performance and reductions in chronic pain seen in the irradiated athletes ignited controversy to whether vitamin D supplementation could constitute as ―athletic unfairness or ―doping (1). Since then, more sophisticated studies have associated vitamin D status with athletic performance indicators such as increased strength, power and cardiorespiratory fitness.
The identification of vitamin D receptors (VDRs) in skeletal muscle suggest that skeletal muscle is a target organ for vitamin D, and it may also explain the association between vitamin D and strength, power, and speed performance (3). VDRs activate intracellular signaling pathways also involved in calcium handling, signaling and myogenesis. Additional correlations have been made between Vitamin D and an increase in size and number of fast twitch muscle fibers, which contribute to short and explosive power (1).
Additionally, new research suggests vitamin D concentrations to be positively associated with cardiorespiratory fitness. One study in particular examined vitamin D concentrations of 163 healthy Caucasian males and females. VO2 max and anaerobic threshold were measured through a cardiopulmonary exercise test. The study concluded that individuals with vitamin D concentrations >30 ng/ml had a higher VO2 max and a higher anaerobic threshold (4).
Testing and Appropriate Dosing
It is important to note that the evidence only supports improvement in vitamin D deficient athletes (<50 ng/ml), which is more common than previously thought. In fact, it is estimated that over ¾ of the population in North American is vitamin D deficient. Endogenous vitamin D synthesis and bioavailability is influenced by many factors, such as season, pollution, cloud coverage, sunscreen, time outdoors, systemic inflammation, eating habits, fat malabsorption, skin coverage, melanocyte concentration, and even body composition (5).
That said, it is imperative to get lab testing to dose appropriately, and check every 3 months until desired levels are reached. Supplementing with someone who already has high vitamin D stores can be hazardous to their health. Vitamin D toxicity can lead to a range of symptoms such as nausea, vomiting, poor appetite, constipation, headache, bone pain, weakness, apathy, and even calcification of arteries. A desired range for athletic performance is 50-70 ng/ml. As a starting point, 35 IU/lb is a good place to start on dosing. In a person with adequate Vitamin D levels, dosing of at least 1000 IU/day particularly through fall and winter months is required to maintain serum concentrations (6).
Quality of Vitamin D
This article wouldn’t be complete without a special note on the importance of vitamin D quality. Most dietary supplement manufacturers purchase vitamin D from raw material suppliers as premixed dilutions, meaning the vitamin (in powder form) is mixed with other powdered substances that, in turn, make it easier for the manufacturer to handle and mix a larger quantity of raw material. Unfortunately the powdered substances used in these premixed dilutions frequently contain potentially detrimental ingredients such as lactose and/or the preservatives BHT, BHA, sodium benzoate, and sorbic acid – all of which are not required to disclose on the product label. ThorneFX does not purchase pre-mixed dilutions of vitamin D. Instead, they use their own vitamin D dilution using pure, hypoallergenic powders, such as magnesium citrate and plant cellulose. The resultant pre-mixture is then added to the dietary supplement being made, ensuring the proper amount of vitamin D is contained in each capsule.
The take-home message is that vitamin D can have a profound effect on health, and maximize athletic potential when deficiency is corrected. Lab testing is a necessity to dose appropriately and reach the ideal vitamin D range of 50-70 ng/ml. Quality of the vitamin D source is also important, and can eliminate unnecessary fillers.
- Cannell, J. et al. Athletic Performance and Vitamin D. Med Sci Sports Exerc. 2009. 41(5): 1102-1110
- Tavera-Mendoza, L. and White, J. Cell defenses and the sunshine vitamin. Sci Am. 2007. 297(5): 62-72.
- Simpson, R. et al. 1985. Identification of 1,25-dihydroxyvitamin D3 receptors and activities in muscle. J Biol Chem. 280(15): 8882-8891.
- Mheid, I. et al. 2009. Vitamin D levels are associated with exercise capacity and measures of endothelial function in healthy humans. 120, S551.
- Webb, A. Who, what, where and when-influences on cutaneous vitamin D synthesis. Prog Biophys Mol Biol. 2006. 92(1):17–25.
- Pazirandeh D and Burns DL. 2014. Overview of Vitamin D. Uptodate. Wolters Kluwer Health.