What is Vitamin D?
Vitamin D is a fat soluble vitamin that maintains bone, muscle and teeth health. It has important interactions with calcium, magnesium and phosphate.While Vitamin D is present in some foods such as red meat and egg yolks, the most efficient way to get enough Vitamin D is through exposing the skin to sunlight... this leads us into our problem!
Vitamin D Deficiency
Vitamin D deficiency is a widespread problem that has been investigated world-wide (1, 2, 3, 4) and is largely attributed to inadequate exposure to sunlight (5). In the modern world, many of us work and study indoors for most of the day. In many parts of Europe and North America, this means that there are extended periods of time where we get very little, if any, sun exposure.Symptoms of Vitamin D deficiency include:
- Fatigue
- Bone Loss
- Hair Loss
- Low Mood/Depression
Table 1 – Guidelines for Vitamin D Consumption (source: ref 14).
| Amount (nanograms) | Outcome |
| >100 | Excess |
| 30-100 | Sufficiency |
| 20 to <30 | Insufficiency |
| 10 to <20 | Deficiency |
| <10 | Severe Deficiency |
Vitamin D and Athletic Performance
In the sporting world there has been an increased interest in the influence of vitamin D on athletic performance. Research suggests that a deficiency can result in negative effects on musculoskeletal health, with increased risk of injuries such as stress fractures (7). A UK study found a positive correlation between vitamin D levels and the height, velocity and power of jumps performed by adolescent girls (8). More specifically, a vitamin D receptor cell has been identified within muscle cells, meaning that vitamin D has a direct impact on muscle tissue (9), but it has also been recognised as playing an indirect role via other structures such as IGF-1 by partially regulating it (10).
The benefits of vitamin D on muscle tissue have been recorded, although findings have been inconsistent. For example, El-Hajj et al (11) conducted a one year, controlled trial of 179 women in two groups; low and high dose vitamin D. The individuals with high vitamin D supplementation had increased lean mass and bone mass but the findings were not repeated in a similar study of male participants.
Further evidence comes from research on older people. A recent experiment suggested Vitamin D may have a role in moderating the age related decline in muscle function (12) but a review of controlled trials exploring vitamin D and calcium supplementation, concluded there was no evidence that vitamin D alone improved the strength or physical function of elderly people (13).
Our Comments
The evidence regarding vitamin D and its positive effect on athletic performance is increasing; it clearly has strong potential for improving muscle mass and preventing injury. In winter, it is thus essential to consume sources that are rich in vitamin D (salmon, sardines, milk, eggs, fortified dairy products) but for those of us who are either time poor or money poor (or simply too lazy), then a high quality vitamin D supplement will also do the job. Unlike some other vitamins, vitamin D is fat soluble therefore the body can store it for a long period of time, storing it in the liver when it is has not been utilised meaning you won’t become deficient quickly if you have a healthy store already.
As with most vitamins and nutrients, there is no consensus amongst organisations regarding the required dosage of vitamin D. According to scientific research (14) however, the performance enhancing benefits of vitamin D can be achieved by consuming doses of 5000-10000IU’s daily for the first couple of weeks for people that are deficient and between 1000-2000IU’s (25ng/0.025mg – 50ng/0.05mg) daily thereafter.
At worst, if vitamin D doesn’t impart performance benefits for everyone, one can feel at ease knowing that they will still have a whole host of other benefits, including increased calcium absorption, reduced risks of cancer, diabetes and multiple sclerosis, better foetal health during pregnancy, as well as improved mood and memory (14, 15).
