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Vitamin D and Sporting performance: whatís the latest?
By: Kellie Hogan (profile)
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Vitamin D is a vital cog in the process of calcium absorption from the gut and therefore optimising bone health throughout an individualís life span.

In recent articles, I have had you thinking about your calcium intake and your iron intake. In this article, we are going to concentrate on Vitamin D which is a bit of a buzz nutrient at the moment. Vitamin D is a vital cog in the process of calcium absorption from the gut and therefore optimising bone health throughout an individual’s life span. Vitamin D deficiency is responsible for rickets in children and can contribute to an increased risk of osteomalacia (soft bones) in adults and osteoporosis in older adults and the elderly.

Vitamin D is mainly sourced via sunlight, a small amount through dietary intake and supplemental intake. Vitamin D occurs in two forms – that which we receive from some foods (D2) and that which is produced when our skin is exposed to UVB radiation from sunlight (D3). Foods containing Vitamin D include; oily fish (salmon, herring, mackerel), margarine and some fortified milks. For example, in Australia, it is not possible to meet Vitamin D requirements through food alone. This would be the same for most countries. Interestingly, recent research has uncovered a high prevalence of deficiency, even in highly sun exposed countries like Australia. Vitamin D deficiency is considered one of the more common deficiencies world-wide at present.

You might think as golfers that you are regularly in the sun, so Vitamin D deficiency is unlikely to be a problem for you. But this may not be the case. Let’s read on.

Australian studies assessing the Vitamin D status of young adults in Australia with casual exposure to sunlight have found rates of marginal Vitamin D deficiency of up to 43%. The Geelong Osteoporosis study found that by the end of winter, 8% of the young women involved in the study (age 20 - 39 years) had a more severe Vitamin D deficiency than they did at the beginning of winter.

As mentioned previously, given the marginal amounts in food, we do rely mostly on sun exposure for Vitamin D. But it is not just those who spend most of their lives indoors that are at risk of Vitamin D deficiency. Even healthy people who spend time outdoors can be Vitamin D deficient if they are covered up with clothing due to cultural or religious requirements about skin exposure or if they cover up and use lots of sun protection (hats, clothes, sunscreen, umbrellas) often due to the very valid concern about developing skin cancer. This is particularly the case for golfers who understandably cover up and apply sunscreen as is the advice to limit risk of sun cancer.

So, we have established that we require adequate Vitamin D for bone health. Let’s look at this a little more closely. Vitamin D maintains blood calcium concentrations so that it is deposited in the bones, helping to maintain strength and density. But we now understand that vitamin D is important for so much more when it comes to keeping our body fit and strong. Vitamin D may play a part in a number of important functions including; 

  • Maintaining a healthy immune system, thus keeping you on the course and less time on the sidelines due to illness;
  • Protecting against respiratory infections;
  • Optimising muscle function by increasing muscle strength and stability; 
  • Healthy skin;
  • Diabetes (low vitamin D results in impaired insulin secretion;
  • Multiple sclerosis;
  • Inflammatory bowel disease;
  • Bowel cancer;
  • Breast cancer and
  • Prostate cancer. 

This growing list is an impressive advertisement for giving a little bit more consideration to Vitamin D. Much more research is required to determine the optimal dose of circulating Vitamin D for the above conditions. In fact, more than 1000 human genes are responsive to vitamin D.

Evidence also indicates that Vitamin D supplementation amongst those who are deficient improves athletic performance. The activated form of Vitamin D produced by our body is a secosteroid which regulates many human genes. As far back as the 1950’s, German literature was suggesting that UVB radiation from sunlight (from which our body produces Vitamin D) improved athletic performance. This effect has been replicated in studies throughout the subsequent decades. Vitamin D also seems to increase the number of type 2 (fast twitch) muscle fibres. These are the muscle fibres that fire more rapidly producing more strength and speed.

What is considered a healthy level of Vitamin D in the blood is hotly debated. However, most seem to agree we should have a blood level of at least 50nmol/ L, although some experts believe we may need a bit more.

Our best source of vitamin D is sunlight. But how much sun is enough? That depends on where you live, the time of the year and how dark your skin is. The table outlines recommended sun exposure times for adequate Vitamin D in Australian capital cities. These times are for exposure of 15% of your body surface to the sun (face, arms and hands). The recommendations are for those with fair skin. The needs of those with highly pigmented skin may be up to 3 times higher. Exposure to sunlight is the middle of that day, particularly the summer months, is not recommended due to the potentially cancerous effects associated with sun exposure at this time. 

Regional recommendations for Sun exposure times for adequate vitamin D in Australia

City

Summer

10am or 2pm

Winter

10am or 2pm

Cairns

6-7 minutes

9-12 minutes

Brisbane

6-7 minutes

15-19 minutes

Perth

5-6 minutes

20-28 minutes

Adelaide

5-7 minutes

25-38 minutes

Sydney

6-8 minutes

26-28 minutes

Melbourne

6-8 minutes

32-52 minutes

Hobart

7-9 minutes

40-47 minutes

Adapted from Vitamin D and Adult Bone Health in Australia and New Zealand: A Position Statement.  MJA, 2005.

Summary for adequate Vitamin D

 

  • Make sure you head outside during sunlight hours most days.
  • Avoid the harsh sunlight of the middle of the day. It is still extremely important to protect yourself from skin cancer.
  • If you are worried that you may not be getting enough sun exposure, get your vitamin D levels checked by your doctor.

Vitamin D supplementation should only be necessary for those with suboptimal levels in their blood. As with all supplementation, care should be taken to ensure excessive doses do not cause adverse consequences. If you think supplementation is necessary, it is important to discuss it with your Sports Doctor. Check your sources of Vitamin D closely and other nutrients that might be in the supplement. For example, while Cod Liver Oil is high in Vitamin D, it also contains Vitamin A which can also be ‘toxic’ at high doses.

Vitamin D is now known to be more than just important to prevent osteoporosis. It plays a role in supporting the healthy function of many of our body’s systems. Improving Vitamin D status has the potential to improve their health and athletic performance. For those who spend many daytime hours indoors and then cover up when outside, it is important to think about whether you are likely to be getting enough Vitamin D.

 

Kellie Hogan

Dietitian/Nutritionist APD

Advanced  Sports Dietitan

B Hlth Sci. (Nutr&Diet) (Hons)

Grad Dip. Sports Nutrition (IOC)(Hons)

 

 

For more information check out the  Sports Dietitians Australia website www.sportsdietitians.com and the Australian Institute of Sport’s website at www.ais.org.au/nutrition.

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