New advice released by the Scientific Advisory Committee on Nutrition (SACN) and Public Health England (PHE) has suggested that we all need a daily intake of 10 micrograms of vitamin D. So what function does the vitamin play, what are the main sources, and which genotype is at the highest risk of being deficient?
Vitamin D and Health
Vitamin D is a regulator of phosphate and calcium in the body, and is needed to grow and maintain healthy bone, teeth and muscles. Deficiency in this vitamin can lead to severe bone pain and muscle aches known as osteomalacia in adults, and in extreme cases, to rickets in children. This is a condition when bones are not strong enough to support growth and become bent and deformed.
Vitamin D and Physical Performance
Research has shown that vitamin D levels can affect physical function and athletic performance. A study on more than 900 people aged over 65 found that those with lower vitamin D levels had poorer physical functioning when tested on walking speed, ability to stand from a chair and to maintain balance.
A meta-analysis of research carried out on 2,313 athletes showed that 56% of them were vitamin D insufficient – with those who trained indoors at greatest risk. There was evidence that daily supplementation of the vitamin helped to increase VO2max, as well as improving sprint times and vertical jump heights, although a weekly dosage did not result in the same improved performance.
Sources of Vitamin D
This crucial vitamin is found in only a few foods. Oily fish and egg yolk are the richest sources of vitamin D in our diets, as they each contain around 10 micrograms per 100g. Red meat also contains small amounts of vitamin D, and milk and breakfast cereals are often fortified with it. However, most people find it difficult to meet the 10 microgram per day quota with a healthy balanced diet alone.
So how do we usually get enough vitamin D? When exposed to sunlight, the skin is able to synthesise the vitamin itself. Although it is impossible to quantify how much time in the sun is needed to allow the body to produce enough vitamin D, short bursts of sun are enough for most people to make all the vitamin D they need in summer. However, health organisations such as the SACN and PHE are keen to remind us that there is an inherent risk of skin damage and cancer when too much time is spent directly exposed to ultraviolet radiation – whether that’s from the sun, tanning beds or lamps. This source of vitamin D is made scarce in winter, as a lower sun in the sky means that less UVB radiation reaches the earth, preventing your skin from synthesising enough of the vitamin.
Recent research published in the New England Journal of Medicine suggests, staggeringly, that almost 50% of the population worldwide is deficient in vitamin D. This spans all ethnicities and age groups, some of which are at greater risk of vitamin D deficiency than others. Having darker skin is likely to put you at higher risk of vitamin D deficiency, since you’ll need to spend more time in the sun to generate an equivalent amount of the vitamin. You’ll also be part of this at-risk group if you spend long periods of time confined indoors, if you cover your skin for cultural reasons, if you are overweight, obese or aged over 65.
Vitamin D and Genetics
At FitnessGenes, we analyses two genes that impact your individual vitamin D levels, VDR and HERC2. If you are a carrier of the AA variation for HERC2 (the melanin production gene), you are genetically at the greatest risk of vitamin D deficiency and should pay especially close attention to the recommendations published by SCAN and PHE.
Vitamin D intake is included in the supplement section of your FitnessGenes Action Blueprint. The Action Blueprint identifies your optimal training, nutrition and physiological strategies as based on your genetic results, to help you maximise your fitness results.
Maintaining Healthy Levels
Supplementation has previously been recommended as the best way for at-risk groups to ensure they are maintaining healthy levels of vitamin D. Leading health organisations have highlighted that it is especially important to add vitamin D supplements to your diet in Autumn and Winter, as sun exposure is often limited during these months.
Many forms of vitamin D exist, with vitamin D3 the most effectively used in the body. The vitamin comes in many forms (it’s also often added to cod liver oil) and can be taken at any time of day.
So although it might seem strange discussing this in the middle of summer, new research suggests that we shouldn’t be shy with vitamin D when the sun makes itself scarce.
Farrokhyar, F., Tabasinejad, R., Dao, D., Peterson, D., Ayeni, O.R., Hadioonzadeh, R. and Bhandari, M., 2015. Prevalence of vitamin D inadequacy in athletes: A systematicreview and metaanalysis. Sports Medicine, 45(3), pp.365378
Association between vitamin D status and physical performance: the InCHIANTI study. Houston DK1, Cesari M, Ferrucci L, Cherubini A, Maggio D, Bartali B, Johnson MA, Schwartz GG, Kritchevsky SB.