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Imagine if you could improve your physical fitness, lower your body fat percentage and decrease your chances of injury and illness; all from just sitting in the sun? Most people would do so, especially in a sun blessed country such as Australia, however, it may surprise you that over a third of Australians don’t take full advantage of this easy and effective way to improve their health and their exercise performance. What we’re talking about is getting enough vitamin D, an increasingly interesting and important essential nutrient.

What Is Vitamin D?

Vitamin D is an essential fat soluble nutrient that is critical for optimal human health. Found naturally in foods such as fatty fish, eggs and fortified in margarine and oil based spreads, a good majority (around 90-95%) of our vitamin D requirements is actually met through exposure to the sun. Through contact with UVB rays, a cholesterol like compound in our body known as 7-dehydrocholesterol converts into Vitamin D3 (cholecalciferol). However the consistent use of sunscreen and the increasing time spent indoors has resulted in a growing number of people who are insufficient in their vitamin D levels.

Vitamin D Deficiency - A Growing Concern

So it seems that there’s a mini epidemic in people who are insufficient in or have low vitamin D levels, especially in Western countries and countries away from the equator and the tropics. The biggest problem by far is the growing trend of spending time indoors which limits your ability to get enough UVB radiation to assist with the production of vitamin D. Even exposure to sunlight through windows is inadequate as glass can almost completely block out UVB rays. Those most at risk of low vitamin D status include:

  • People who often use sunscreen
  • Obese/overweight individuals
  • Elderly living in aged care facilities
  • Modest dressing individuals
  • Office workers
  • Darker skinned individuals

However, it’s surprising that some studies (Forney 2013) have been able to show even young, physically active individuals who appear to have plenty of exposure to direct sunlight seem to have lower vitamin D levels. This might suggest that there seems to be a very individual response to vitamin D production with exposure to sunlight, beyond that of skin colour and clothing and that low vitamin D levels may be more prevalent than ever before.

Low Vitamin D - Side Effects

Low vitamin D levels have been correlated with a wide variety of diseases and health issues including:

  • Increased Risk of Falls
  • Cardiovascular Disease
  • Several Cancers
  • Bone Fracture Risk
  • All Cause Mortality
  • Poor Glucose Metabolism

Low Vitamin D & Exercise Performance

In addition to the above health issues, there’s recently been interest in the connection between vitamin D status and exercise performance. Close et al (2013) were able to show that when vitamin D deficient athletes were supplemented with vitamin D3 over a course of 8 weeks, their exercise performance in terms of sprint times and vertical jump distance increased. Forney et al (2013) were able to show differences in physical fitness in healthy, physically active young individuals, with those who had high vitamin D levels with better fitness than those who had lower vitamin D levels. In fact, participants who had a higher serum level of vitamin D had on average 20% greater VO2max than those who were considered vitamin D insufficient. However, it’s not just athletes and physically active individuals who benefit. Carillo et al (2012) found that supplementing obese/overweight individuals participating in a weights program improved their power output, while the placebo group had no improvements. So there seems to be a link between vitamin D levels and physical performance, which occurs in a wide variety of individuals with varying fitness levels and body compositions.

Low Vitamin D, Obesity & Body Fat

It has also been noted that there may be an association between vitamin D levels, obesity and body fatness with studies (Vimaleswaran 2013) showing a causal relationship where rises in body mass index being correlated with a drop in vitamin D levels in the body. This correlation is further cemented through an intervention study (Salehpour 2012) which showed that obese and overweight women supplemented with vitamin D was able to reduce their fat mass, independent of any body mass changes. However, it seems that higher levels of supplementation may actually increase body fat accumulation (Carillo 2012). While the evidence is still inconclusive on vitamin D status and body fat levels, it would still be prudent to have adequate rather than inadequate stores of vitamin D.

Vitamin D, Testosterone & Sexual Health

There have also been studies examining the correlation between vitamin D status and testosterone levels. Pilz et al 2011 was able to show that men with abnormal testosterone levels also had lowered serum vitamin D levels and when supplementation was given, both vitamin D levels were normalised and testosterone levels were improved significantly by a whopping 25.2%. Vitamin D has also been connected with sperm health, however interestingly, there appears to be a specific range in which sperm health parameters are at their most optimal. Improving testosterone levels is important for muscle mass growth and being able to do so through simple means such as standing in the sun makes it a very attractive and cost effective solution and one every trainer should be taking advantage of.

Vitamin D Daily Requirements

Different countries have different recommendations for vitamin D intake with Australia’s National Health and Medical Research Council advocating a small 5μg/day (200 IU) while the US recommends three times that with 15μg/day (600 IU). However, there have been experts in the field (Heaney et al 2011) who suggest that even this level is too low, stating that physiologically humans are able to produce between 100-300μg/day (4000-12000IU) through sun exposure alone and common upper tolerable limits of 100μg/day or 4000IU is not biologically plausible. Regardless, it seems that achieving 25-50μg/day or 1000-2000IU/day seems to help most of the population reach blood or serum levels of vitamin D that is seen to be optimal for bone health in older individuals. There is also a view that athletes may require more, however the evidence is still inconclusive.

Vitamin D Foods & Sources

So knowing how much vitamin D you need is one thing, the other is knowing how to get it. As previously mentioned, for most people, most of their daily requirements for vitamin D are met through sun exposure. Here are the recommendations from a recent Australian and New Zealand position statement from Nowson et al (2012):

  • For moderately fair-skinned people, a walk with arms exposed for 6–7 minutes mid morning or mid afternoon in summer.
  • For moderately fair-skinned people, a walk with as much bare skin exposed as feasible for 7–40 minutes (depending on latitude) at noon in winter, on most days, is likely to be helpful in maintaining adequate vitamin D levels in the body.

If sun exposure is not possible, supplementation through increased intake of high vitamin D foods such as fatty fish and UV light treated mushrooms or through a vitamin D supplement is possible.

Vitamin D - A Potent Anabolic & Ergogenic Agent

There is increasing evidence to suggest that Vitamin D may help assist and improve exercise performance, physical performance, muscle growth, testosterone levels and body composition parameters – all important factors for any athlete, bodybuilder or casual exerciser. With multiple health benefits associated with increased vitamin D levels and considering the extent of vitamin D insufficient individuals out there; it may be ideal for both active and sedentary individuals to get their vitamin D status checked, achieve some daily sun exposure or to consider vitamin D supplementation. However, it is still important to be sun smart and to know that supplementation should only make up a small part of your mission to achieve improved levels of vitamin D.

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1. Close GL et al. Assessment of vitamin D concentration in non-supplemented professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function. J Sports Sci 31: 344-353 (2013)
2. Forney L et al. Vitamin D Status, Body Composition and Fitness Measures in Younger, Physically Active Individuals. J Strength Cond Res. (2013) Jul 26. [Epub ahead of print]
3. Carrillo AE, et al. Impact of vitamin D supplementation during a resistance training intervention on body composition, muscle function, and glucose tolerance in overweight and obese adults. Clin Nutr. (2012)
4. Vimaleswaran KS et al. Causal relationship between obesity and vitamin D status: bi-directional Mendelian randomization analysis of multiple cohorts. PLoS Med. 2013;10(2)
5. Salehpour A et al. A 12-week double-blind randomized clinical trial of vitamin D3
supplementation on body fat mass in healthy overweight and obese women. Nutr J 11:78 2012
6. Pilz S, et al. Effect of vitamin D supplementation on testosterone levels in men. Horm Metab Res. (2011)
7. Heaney RP & Holick MF. "Perspective: Why the IOM Recommendations for Vitamin D are Deficient". Journal of Bone and Mineral Research 26 (3): 455–7. (2011)
8. Bischoff-Ferrari HA, et al. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr. (2006)
9. Vieth R, et al. The urgent need to recommend an intake of vitamin D that is effective. Am J Clin Nutr. (2007)
10. Nowson CA et al. Vitamin D and health in adults in Australia and New Zealand: a position statement. Med J Aust. 2012 Jun 18;196(11):686-7.
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