Vitamin D was once thought to influence little more than bone diseases such as osteoporosis and rickets. However, it is now recognized as a major player in overall human health. Vitamin D is involved in so many physiological functions that it’s easy to wonder if there is anything this fat-soluble vitamin does not do.


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. It 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). Above all, this is one of the primary reasons why Vitamin D can impact such a wide variety of diseases, including:

Cancer Hypertension Heart disease
Autism Obesity Rheumatoid arthritis
Diabetes 1 and 2 Multiple Sclerosis Crohn’s disease
Flu Colds Tuberculosis
Septicemia Aging Psoriasis
Eczema Insomnia Hearing loss
Muscle pain Cavities Periodontal disease
Athletic performance Macular degeneration Myopia
Pre-eclampsia Seizures Fertility
Asthma Cystic fibrosis Migraines
Depression Alzheimer’s disease Schizophrenia


Vitamin D and Athletic Performance

Not surprisingly, Vitamin D can have a strong impact on athletes as well. For example, in the early 20th century, Russian and German researchers used sunlamps to stimulate Vitamin D production in their elite athletes. The increase 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). Furthermore, VDRs activate intracellular signalling pathways also involved in calcium handling, signalling and myogenesis. Additional correlations have been made between Vitamin D and increase in size and number of fast twitch muscle fibres, which contribute to short and explosive power (1).

Finally, research suggests Vitamin D concentrations to be positively associated with cardiorespiratory fitness. For example, one study in particular examined Vitamin D concentrations of 163 healthy Caucasian males and females. Cardiopulmonary exercise tests then measured VO2 max and anaerobic threshold. In conclusion, the study found that individuals with vitamin D concentrations <30 ng/ml or <75 nmol/L, had a higher VO2 max and 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 or <125 nmol/L), which is more common than previously thought. Researchers have estimated that over 3/4 of the population in North America is Vitamin D deficient. Endogenous Vitamin D syntheses 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. This should be repeated every 3-4 months until desired levels are reached. Supplementing with someone who already has high Vitamin D stores can be hazardous to their health. Unfortunately, Vitamin D toxicity can lead to a range of symptoms such as nausea, vomiting, poor appetite, constipations, headache, bone pain, weakness, apathy, and even calcification of arteries. A desired range for athletic performance is 50-70 ng/ml or 125-175 nmol/L. A good place to start dosing is 35 IU/lbs. In a person with adequate Vitamin D levels, dosing of at least 1000 IU/ day particularly through the fall and winter months is required to maintain serum concentrations (6).


Vitamin D May Not Be Enough

Most people are unaware that supplementing with just Vitamin D may not be sufficient, and may even be dangerous. Firstly, the body needs magnesium to activate Vitamin D and the majority of the population is deficient. Over the past 50 years our soil has become increasingly depleted and it is difficult to get through diet alone. Serum magnesium levels are also decreased with stress, certain medications, inflammation, poor diet, and strenuous exercise – making athletes particularly vulnerable (7). Secondly, it is prudent to take Vitamin K2 when taking high doses of Vitamin D. If supplementing with Vitamin D without sufficient K2, calcium can accumulate in soft tissue and even contribute to cardiovascular disease and atherosclerosis (8)


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. It is often a premixed dilutions, which frequently contain potentially detrimental ingredients.  Companies are not required to label ingredients such as lactose and/or the preservatives BHT, BHA, sodium benzoate, and ascorbic acid. It’s best to talk to your Naturopath about the best sources for you during the winter months.


Bottom Line

In conclusion, Vitamin D can have a profound effect on health and athletic potential can be maximized when deficiency is corrected. Lab testing is not OHIP covered except with a few key pathologies, but it’s worth paying and checking your status. However, note that just taking Vitamin D may not be enough. It’s helpful to work with a Naturopath so they can guide you on brands, dosages and Vitamin D co-factors tailored to your specific needs.

If you’re curious about Naturopathic Medicine, or would like to optimize your health through thorough blood work and an evidence based treatment plan – you can book a complimentary 10 minute discovery call to see if we’re a good fit.





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