Elizabeth Broad: Optimising vitamin D status

This blog represents the views of Team USA’s Elizabeth Broad, Senior Sports Dietician

Vitamin D is a prohormone (mistakenly labelled as a vitamin) which has long been known to help the absorption and uptake of calcium into bone, thereby being important for bone density.

Low vitamin D results in osteomalacia and rickets, a disease of ‘soft’ bones which results in bowed legs. Vitamin D is fat-soluble and therefore found in some foods, especially oily fish. However, our primary source of vitamin D is conversion of UVB sunlight through the skin.

More recently, it has been found that there are vitamin D receptors in various body organs – muscle, bone, the brain – which has given rise to interest in other roles of vitamin D throughout the body.

There is now evidence that vitamin D levels influence muscle strength, inflammation, immune function, and mood state – all of which can influence sports performance.

Furthermore, concerns have been raised about the incidence of low vitamin D status which appears to be increasing (estimated over one billion people worldwide) even in countries where sunlight exposure is consistently available (partly due to increased use of sunscreen).

Vitamin D status varies with geographical location (people living in higher latitudes more likely to have low vitamin D status), season (vitamin D levels are lower at the end of winter than at the end of summer), and skin colour (darker skin colour absorbs less vitamin D).

Preliminary studies in Paralympic athletes have indicated that the incidence of low vitamin D status is at least as high, if not higher, than in able-bodied athletes with spinal cord injured athletes at highest risk.

Risk factors include:

• Participation in indoor sports

• Participation in winter sports

• Darker or extremely fair skin colour

• Living/training at the more northern or southern latitudes

• Covering the whole body with clothes (arms and legs) or otherwise limiting sun exposure

• Low dietary vitamin D intake

• Use of high SPF factor sunscreen

Signs and symptoms of vitamin D deficiency

• Low bone mineral density (Z score < -1 for spine or proximal femur)

• Stress fractures

• Fatigue

• Unexplained muscle and joint pain

• Frequent illness

What to do?

1. Get your vitamin D status assessed – this requires a blood test. The normal range is 30-80 ng/mL (75-200 mmol/L).

2. If your levels are lower than the normal range and/or you have a number of risk factors, discuss with your doctor the most appropriate vitamin D supplementation to use.

3. Ensure you consume as much vitamin D rich foods as possible. Useful food sources include oily fish (e.g. salmon, sardines), cod liver oil, fortified food products (some countries fortify dairy, juice or some cereals) and certain types of sundried mushrooms (check the label).

4. Get a safe level of sunlight exposure – guidelines will vary between countries and depending on the season, but in summer this would equate to roughly 10-15 minutes per day without sunscreen, exposing as much skin surface area as you can. The duration is usually longer in winter (up to 30 minutes per day). More is required for darker skin colours.