We know vitamin D is a unique nutrient by its sheer nature of endogenous synthesis. When the skin is exposed to ultraviolet-B radiation, pre-vitamin D3 is produced. Pre-vitamin D3 then undergoes transformation into vitamin D3 (cholecalciferol) over a period of 2 to 3 days. Vitamin D3 then travels to the liver and is metabolised by cytochrome P-450 enzymes before the kidneys convert D3 to its active form 1,25(OH)2D. This final activation stage is driven by parathyroid hormone (PTH) when serum calcium and phosphate concentrations fall. Vitamin D is so important to the body, immune cells, brain, colon, breast, and other cells have the ability to also activate vitamin D locally when required. Typically, we obtain 80% of our vitamin D from the sun and 20% from food sources.
Why is vitamin D important?
Vitamin D plays an important role in an athlete’s health, training and performance. Specifically, it is now recognised that vitamin D is imperative for bone health, immune function, hormonal balance, mental health and inflammatory modulation.
Vitamin D functions as a modulator of up to 1000 genes involved in cellular growth, immune function and protein synthesis. In this role, the active form of vitamin D interacts with receptors in the intestine, bone, brain, heart, immune cells and skeletal muscle.
Studies show it may even be necessary for optimal muscle function and performance as muscle performance is impaired by suboptimal vitamin D status. Deficiency induces atrophy of fast twitch muscle fibers, impairs calcium uptake and prolongs time to peak contractile tension and relaxation. Studies also show Vitamin D deficiency may delay rehabilitation from injury.
In sporty pregnant women, low vitamin D levels are linked to pre-eclampsia, gestational diabetes and adverse pregnancy outcomes. Vitamin D also plays a part in regulating insulin, blood sugar balance and thyroid hormones. Research shows that a deficiency of vitamin D is associated with a high risk of thyroid antibodies, which are found in individuals suffering with autoimmune thyroid disorders.
Vitamin D upregulates gene expression of antimicrobial agents in our first line of immune defense and boosts our respiratory protection. It also down regulates inflammation. In one study of athletes, poor vitamin D status was associated with increased frequency of infections including the common cold, influenza, and gastroenteritis when vitamin D levels dropped below 40 nmol/L.
Vitamin D is most commonly known in the athletic community for its influence on bone health and prevention of bone injury. Vitamin D influences bone health by upregulating expression of genes that enhance intestinal calcium absorption, and reabsorption by the kidneys along with increasing bone building cell activity. Studies show calcium absorption significantly increases when vitamin D levels are sufficient. Calcium absorption is reduced to 10-15% with low vitamin D levels and stress fracture risk significantly increases.
Factors contributing to low vitamin D
In a peer review research paper published by the American College of Sports Medicine, Larson-Meyer and Willis (2010) propose low vitamin D levels in athletes occurs primarily due to insufficient direct UVB exposure (due to smog, cloud cover or latitude), early- or late-day training, indoor training, geographic location further away from the equator and sunscreen use (SPF of 15 lowers vitamin D synthesis capacity by 98%).
Low body fat may also contribute to low vitamin D levels as vitamin D is stored in fat cells. In clinical practice we also see low vitamin D levels associated with low magnesium as magnesium is a co-factor for vitamin D binding protein. The conversion of vitamin D to its active form is also a magnesium dependent process. Disruption to the microbiota and gut inflammation may also affect the availability of vitamin D. In addition some patients may find it difficult to increase their vitamin D levels if they have low antioxidant status. Vitamin D levels may also be lowered by drugs such as anticonvulsants, corticosteroids, cimetidine, theophylline, or the weight loss drug orlistat.
Symptoms of vitamin D deficiency
- Skeletal pain and weakness are early symptoms of vitamin D deficiency. One relatively recent study found 93% of individuals with persistent nonspecific musculoskeletal pain had low vitamin D levels.
- Stress and other bone fractures
- Bone pain
- ‘‘Heaviness in legs’’
- Chronic injury
- Frequent illness
- Photo sensitivity
- Pale floating stool
5 easy steps to prevention and treatment of vitamin D deficiency
- Get your vitamin D levels checked biannually- before winter and again in spring. As a general guide, Osteoporosis Australia recommends most people should have a vitamin D level of at least 50 nmol/L at the end of winter, which means people may have higher levels during summer (60-70 nmol/L). However, in order to maintain optimal health, athletes should aim for serum levels over 90nmol/L ideally between 100 and 130 nmol/L.
- Athletes living in southern states of Australia and New Zealand need 30 minutes of direct skin exposure (springtime) on large areas of skin such as back, arms, chest or legs closer to midday. Athletes living closer to the equator may require 15 minutes before 10 am. During this time avoid putting sunscreen on, then for the rest of the day, cover up.
- Consume vitamin D rich foods on a daily basis such as oily fish like cod, salmon, sardines or tuna, egg yolks, sun-dried mushrooms, and fortified milk, butter and fortified cereals. Some patients may benefit from cod liver oil which is high in vitamin D and A and essential fatty acids.
- When levels are low, take a quality vitamin D supplement in the correct dosage range and a probiotic. Certain probiotics such as Lactobacillus rhamnosus LGG and Lactobacillus plantarum enhance Vitamin D receptor expression.
- Obtain adequate magnesium rich foods such as spinach, pumpkin seeds, almonds, black beans, oyster mushrooms, avocado, figs, yogurt or kefir and banana. Chocolate also contains magnesium. See our delicious chocolate bean slice recipe here .