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Column 33, October 2010
Vitamin D deficiency may reduce health and performance – are you at risk?
Benefits of Vitamin D
Vitamin D plays a well-known role in bone health by helping the body to absorb calcium in the small intestine. Perhaps less well-known however is it’s importance for muscle strength, as well as it’s vital role in supporting the immune system.
There are also now indications that vitamin D may have a much broader health role – those with lower levels show a greater association with colon cancer, high blood pressure, type 2 diabetes, periodontal disease and poor lung function, though the jury
is still out as to whether or not higher vitamin D levels would help protect us from these diseases.
Vitamin D deficiency in the NZ population, and running population
Measurement of serum vitamin D levels in population samples has revealed an unexpectedly high prevalence of vitamin D deficiency among children, adults, the elderly and other vulnerable groups in New Zealand.
It is a fallacy that we Kiwis receive adequate vitamin D from casual exposure to the sun. It seems runners are no better off either.
A 2008 study in Dallas found that even those averaging 32km of running a week have low vitamin D levels.
Potential for athletes
Several very recent scientific publications point to vitamin D’s effect on performance. In one particular study it was concluded that adolescents with higher levels of vitamin D can jump higher, quicker, and with greater power than those with lower levels.
However, these observational studies do not prove a direct cause and effect. It is highly likely that vitamin D status may reduce the risk of sports injuries, including stress fractures.
Interestingly enough Deena Kastor (US marathon record holder) was diagnosed with low vitamin D levels shortly after she withdrew from the 2008 Beijing Olympic Marathon with a fractured bone in her foot.
A recently published literature review examined the relationship between vitamin D, UVB exposure and athletics. The author used studies from the 1940’s and 1950’s in which German and Russian athletes received UVB exposure.
These studies suggested UVB may boost performance. Other studies suggest physical performance peaks in summer and declines in early autumn. The author suggested one possible explanation for this link between UVB and performance, was the effect UVB has to increase vitamin D status.
Are you getting enough?
The recommended daily requirement for vitamin D is:
- Adults 19-50 years 5 micrograms (mcg)
- Adults 51-70 years 10mcg
- Adults over 70 15mcg
This daily requirement can be achieved in many ways:
- UV exposure of the hands, face and arms on a daily basis (without sunscreen). The length of exposure required for fair people is approximately 6-9 minutes in summer (outside the ‘peak’ UV hours of 11am-4pm), and 24-40mins in winter (during the peak of day).
Dark skinned people may require 3-4 times this level. These levels are not considered to increase the risk of skin cancer.
Note – excess UV exposure will not only increase your risk of skin cancer and cataracts, it may actually cause the vitamin D produced in your skin to degrade, rendering it useless.
- Dietary sources such as fatty fish (eg salmon), eggs, foods fortified with vitamin D eg some milks and margarines.
Terakihi, 115g (baked) – 5.8mcg
Salmon, 115g (baked) – 5.8mcg
Milk, fortified with Vit D, 250ml – 1.25mcg
Margarine, 2 tsp – 1 mcg
Eggs, 2 – 1.7 mcg
Note: until NZ considers more widespread vitamin D fortification of foods, it is unlikely we will achieve the necessary daily r requirements from food alone.
- Supplementation (tablets or intramuscular injections). Note: these are best prescribed by your doctor, as using fish oil supplements (rich in vitamin D) for example can result in excess vitamin A.
A simple (but expensive) blood test can be carried out by your doctor to check your levels, however your doctor may start you on supplements without first testing, if you are at considered to be at higher risk:
- Elderly (reduced absorption, and lack of sunlight for those in residential care)
- You avoid the sun, or are vigilant with sun block
- Those with dark skin or those wearing veils
- Those with malabsorption (eg coeliac disease…)
- Veganism
Bring on summer I say!
Marnie Oberer
Shoe Clinic are proud to have...
Marnie Oberer as an Expert columnist.
Marnie is a nutritionist and athlete and has been the host of Eating Well on TV One for the past two years. She is a trained dietitian and has a degree and two postgraduate diplomas from the University of Otago.
By 28 Marnie had set up her own business consultancy, advising high performance athletes and teams. Marnie started competitive aerobics and caught the ‘marathon bug’ running in Australia, UK and USA.
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