Recent research on vitamin D deficiency has revealed startling evidence of a high prevalence of deficiency (not insufficiency) across various high-level disciplines.
From professional football to ballet dancers, the realisation that sun exposure is not always the missing link, but may have root causes in Vitamin D Receptor genes and transporters. We are genetically unique and we metabolise and absorb nutrients differently. Deficiencies have been found in swimmers, gymnasts, volley ball players, taekwondo fighters, jockeys, runners, cyclists, and weight lifters.
Vitamin D (VITD) plays a vital role in bone maintenance and is important for preventing stress fractures., but recent evidence has shown its essential role in extraskeletal functions, including skeletal muscle growth, immune and cardiopulmonary functions, and inflammatory responses, which affect athletic performance. VITD is not only a micronutrient, but a pro-hormone too.
VITD is linked to the parathyroid hormone (PTH). These two hormones regulate the concentration of calcium in the blood. Chronic VITD deficiency leads to secondary hyperparathyroidism. The combined effect of VITD deficiency and high PTH levels can cause excessive mobilisation of calcium from the bone to maintain circulating calcium levels at the expense of bone mineral density.
VITD activates genes that influence muscle growth and differentiation, most particularly, in type 2 fast twitch fibres. The receptor for 1.25-OHVITD (vitamin D)is associated with the signalling mechanism that enhances the interaction between myosin and actin in the sarcomere (filaments that make up striated muscle tissue). This interaction is what makes the force of the muscle contraction stronger. (Koundourakis, N.E et al.)
VITD is difficult to obtain in effective amounts from diet alone, because very few foods naturally contain the vitamin, exceptions are livers of fatty fish such as salmon, herring, sardines and red meat. One study (Rankinen, TS et al.) found that only 5% of college athletes met the US RDA for VITD.
Many products are fortified with VITD but the essential process of synthesis may be upset by many environmental, and of course, genetic factors.
Sufficient UVB radiation , sunscreens, clothing, amount of melanin(skin pigment) in an individual's skin as well as geographical location. Dark-skinned athletes are more prone to deficiency and may need up to 10 times longer exposure to UVB radiation.
Willis KS et al. noted that muscle power and force in marathon runners were linked to with VITD levels. Deficiency in VITD increased the risk of muscle myopathy (weakness due to dysfunction), and impaired cross-bridge formation leading to muscle weakness and fatigue.
Optimal supplementation and exposure to ultraviolet light has been shown to improve biomarkers of deficiency. In elite rowers, maximal oxygen uptake (VO2max) increased significantly with a dosage of 6000 iu/day over an 8 week training period and, soccer players given 5000 iu/day over an 8 week training period showed increases in both force and power output. Recovery time and inflammatory markers in physically active adults, showed an improvement with 4000 iu/day.
A resilient immune system is paramount to any hard-training athlete. VITD plays a vital role in immune system function. Upper Respiratory Tract Infections (URTI's) have plagued many competitive athlete's careers.
VITD can reduce the inflammatory response of proinflammatory cytokines such as IL-6 (Interleukin 6) and TNFa (Tumor Necrosis Factor alpha). Athletes with low levels of serum VITD may experience a higher occurrence of URTI's.
In the brain, VITD receptors are present and affect the central and peripheral nervous systems. Within the primary motor cortex that coordinates movement, these receptors play an essential role in athletic performance. An additional mechanism, that impacts Vitamin D Receptors (VDR) and the brain in sports performance may relate to nociceptors. These are sensory nerve cells that react to noxious stimuli by sending signals through the spinal cord and brain. It has been hypothesized that low VITD may result in nociceptive hyperinnervation and hypersensitivity within deep muscle tissue. The 'over-signalling' in the receptors, transfers pain signals to the brain and this in turn results in an inhibitory physical response.
Vitamin D supplementation may therefore, impact neuromuscular performance as well as aerobic and power performance in athletes.
Always consult your health practitioner or GP before self-medicating, it may not always be necessary. Remember, more, is not always best for everyone.