The Low Down on Vitamin D

“Vitamin D deficiency is a major concern to combat sports athletes due to the effect on muscular-skeletal and immune systems. Maintaining sufficient levels of Vitamin D in athletes has been seen to reduce the risk of stress fractures, inflammatory injury, illness, and muscle dysfunction.”

Vitamin D for athletes

The supplementation industry is a dominating force in the world of health and fitness. Athletic and non-athletic populations alike are often convinced through advertising and marketing that they are likely to be deficient in one or multiply vitamins and minerals due to insufficiencies found in modern diets, or simply, promoting the concept of more is better. But are we actually deficient in these vitamins and minerals, and do we really need to supplement?

This article will focus on vitamin D, the sunshine vitamin, the most discussed vitamin during the winter months! This will be the first in a series of articles discussing supplementation, vitamins & minerals and there importance for combat sport athletes. 


 Vitamin D is an important micronutrient linked to bone health, immune system function and optimal muscle function, three vital aspects of a combat sports athlete!

Firstly, Vitamin D plays an essential role in the absorption/reabsorption of calcium by the body and also in bone remodeling, or in simple terms the rebuilding of bone. Bone health is an incredibly important aspect of a combat sports athlete in the prevention of injury, especially when we consider that combat sports training often involves impact and heavy loading to bones and joints of the body. Bone health is of even more importance to females, and female athletes, as they are at increased risk of bone-related injury and osteoporosis, so Vitamin D might be of extra importance in this case.  

Secondly, Vitamin D increases immune function at times of immune suppression. A combat sports athlete in the midst of a fight camp generally has a heavy training load and is often in a caloric deficit, both often resulting in a weakened and suppressed immune system and in turn increasing the risk of illness. Therefore, Vitamin D levels may be a vital component in ensuring an athlete’s immune function is optimal and thus possibly preventing an illness that would negatively impact training and recovery, especially during the winter months.

Vitamin D is also involved in the alteration of inflammation in the body, a very important concept when an athlete is in a period of intense training. Vitamin D, if at sufficient levels,  may aid in the reduction of inflammation which in turn may allow an athlete to recover more efficiently and maintain an intense training load.

Finally, muscle function is also effected by Vitamin D status in its impact on muscle growth and muscle signaling. An obviously incredibly important factor when we are talking about athlete performance and positive adaptations to training!


The primary source of Vitamin D is endogenous synthesize (creation by the body), occurring from cutaneous (the skins) exposure to the sun’s ultraviolet (UV) radiation. Dietary intake is also a contributing factor but in significantly lesser amounts. Dietary sources generally come from the ingestion of food such as fatty fish like salmon, sardines, etc.

An important fact in Vitamin D status of an athlete is that levels can be varied due to numerous factors, such as the season (eg. Winter), hemisphere in which situated, general time spent in the sun and dietary intake.


Vitamin D deficiency is a major concern to combat sports athletes due to the effect on muscular-skeletal and immune systems. Maintaining sufficient levels of Vitamin D in athletes has been seen to reduce the risk of stress fractures, inflammatory injury, illness, and muscle dysfunction.

A study consisting of many research papers investigating Vitamin D inadequacy in athletes found that the occurrence of deficiency was 56% in 23 studies investigating over 2,313 athletes, with substantial increases in locations far from the equator, winter months and indoor sports.

So do all athletes need to Supplement!? The simple answer is NO, not all athletes need to supplement with vitamin D! An athlete should first assess Vitamin D levels by frequent serum testing of 25(OH)D3 concentrations through a blood test from a doctor or private clinic, or if serum testing is not available or too expensive, consider supplementation if sun exposure is severely limited and/or dietary intake is relatively low. Also, supplementation may be very important during fight camp, due to limited caloric intake, heavy training loads and increased risk of illness (especially during winter!)

In the case of deficiencies, the utilization of supplementation is advised by current research for optimal health and in the reduction of injury risk. Although, it should be noted such supplementation is not going to increase performance, as there is insufficient evidence in the support of its use in this way.


In order to cover all the bases to ensure an athletes Vitamin D status is at a healthy range, and for optimal function & recovery,  the best protocol is a mixture of proper sun exposure, between 5 to 30 minutes several time per week to >10% of body’s skin, adequate dietary intake, and supplementation.


In relation to supplementation, Vitamin D3 or D2 (of around 2000 IU per day) has been seen to be effective in increasing Vitamin D levels, with absorption being aided with the co-ingestion of high-fat meals. A Vitamin D supplement can be obtained via the internet and/or pharmacist usually containing general doses of around 1000 IU. The research has found that Vitamin D supplementation has been seen to significantly increase serum 25(OH)D3 concentrations over a 12-week period, providing clear evidence that supplementation is an effective method is raising serum Vitamin D levels.

One important aspect of Vitamin D supplementation is that if the levels of an athlete are adequate, further supplementation with the use of vitamin D2 may have a negative effect on vitamin D levels and therefore should only be used in a case of deficiency. Also, in consideration of “more is better”, there can be negative effects on Vitamin D absorption and levels is very large doses (megadoses) are ingested.

To make it plain and simple, Vitamin D supplementation should be a tool to aid an athlete reach optimal levels. Supplementation is recommended especially during the winter months or when sun exposure is limited and should be considered particularly during a fighter camp!

Jack Doherty – TFD Dietitian


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