During the winter months when the sun is lacking, it has been reported that it is very difficult for UVB rays to pass through the atmosphere and consequently there may not be sufficient UVB radiation to synthesise vitamin D. It has recently been reported that in the U.K. between October and March, synthesis of vitamin D may be almost impossible and therefore, the majority of the UK population may be vitamin D deficient during the winter months. 1 in 3 kids in the UK is vitamin D deficient. A study in Birmingham offered free vitamin D supplements to kids under 5 and to pregnant mothers over a four year period. They found cases of rickets were halved.
Has not been proven but have read three articles stating vitamin D3 reduces body fat. Prehistoric male/female needed more fat in winter to survive, roughly 5%. Lack of sun = lack of vit D3 so message is sent to body to store fat as winter is coming. So more vit D3 = switching off of fat storing gene.
Vitamin D2 in contrast, is mainly derived from the diet, although it must be stated that very few foods naturally contain vitamin D and therefore many foods are fortified with it.
Sources of D2:
cod liver oil
Wild cooked salmon
Mackerel (cooked)
Fortified orange juice
Canned oysters
Mushrooms
Beef liver (cooked)
Egg (whole)
The physiological role of vitamin D in relation to exercise:
BONE HEALTH – for many years it has been noted that vitamin D is essential for optimal bone health through the increased absorption of calcium. Low vitamin D status observed in winter results in a transient fall in bone mineral density, suggesting that individuals may be particularly susceptible to bone problems during hard training in winter. It should be noted that this study was in an older non-trained demographic.
MUSCLE FUNCTION – It has been suggested that restoring adequate vitamin D status may stimulate protein synthesis and improve musculoskeletal performance. Preliminary data suggests that correcting low vitamin D status does improve performance (1RM muscle strength).
IMMUNE FUNCTION – Vitamin D can maintain and enhance immune function during times of intense training when you are susceptible to infection.
The RDA for vitamin D3 in the UK is 400IU found in multivitamins. Many authors suggest this is insufficient. Perhaps the safest option is to consume a vitamin D rich diet utilising some of the foods outlined above. During the winter months consider a 10,000IU supplement in soft gel capsule form (best for absorption) a day for 12 weeks. Higher doses, based on body weight, are in the range of 20-80IU/kg daily.
The most common amount is 14 nanomollles p/litre in the U.K. whilst optimum is 80-120 nanomollles p/litre.
Reference
https://poliquineducation.com/product/applied-biosignature-transformations-online-certification/