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Vitamin D- The Sunshine Vitamin

Updated: Mar 27, 2023

Vitamin D is an important micronutrient to have in our diet. Vitamin D behaves like a hormone which our body cannot make itself and it must be obtained from the diet (1). It is a fat-soluble vitamin which is naturally present in only a few foods. The three sources of vitamin D are sun radiation, diet and supplementation (2). Vitamin D can be synthesised by our skin when exposed to sunlight. Vitamin D plays an important role in stimulating calcium and phosphorus absorption (2). This is essential for teeth and muscle health and prevents bone diseases.

Vitamin D has two main forms D2 (ergocalciferol) and D3 (cholecalciferol). Both forms are absorbed in the small intestine (2). Vitamin D2 is found in plant sources like mushrooms, fortified foods and dietary supplements. Vitamin D3 is found in animal sources like oily fish, liver, egg yolk and butter.

Vitamin D deficiency/ Consequences Of Insufficient Vitamin D

Vitamin D deficiency (a lack of vitamin D in the body) is common in many populations worldwide, especially in countries where there is very little exposure to the sun. In Ireland and the UK especially, during the autumn and winter months from October to March, there is not enough sun exposure for us to absorb the UVB rays, so we don’t absorb vitamin D through our skin (3).

Women are at a higher risk of suffering from osteoporosis due to rapid bone loss after menopause, so ladies its important to maintain as much bone density as possible to reduce the risk of disease later! (5).

People can develop vitamin D deficiency when intakes are lower over time than the recommended levels or when sunlight exposure is limited i.e. during the autumn and winter months. A lack of vitamin D can lead to bone deformities like rickets in children and bone pain called oestomalacia in adults and adolescents. Signs and symptoms of rickets and osteomalacia include pain, seizures, spasms and dental abnormalities.

Vitamin D Requirements

Vitamin D works really well with calcium for healthy bones, muscles and teeth. Vitamin D promotes calcium absorption in the gut and is needed for bone growth and remodelling (1). Insufficient levels of vitamin D may lead to thin brittle bones. The requirements for vitamin D for children from the ages of 1 and adults is 10 micrograms (mcg) or 400IU supplement of vitamin D per day. For babies up to the age of 1 need 8.5-10mcg per day (3).

Food Sources

There are few foods that naturally contain vitamin D. Cod liver oil and oily fish (salmon, mackerel, tuna, sardines, herring) are the best sources of vitamin D, but it is not eaten often by many people. Other sources include egg yolk, red meat, offal, fortified breakfast cereals and fat spreads (1). However, these are all in very small quantities and we need to eat larger amounts of these foods to reach the recommended daily requirements.

Vitamin D supplements are widely available to buy in most supermarkets and health food shops. It is recommended to take a vitamin D supplement especially during the autumn and winter. Babies and children, Pregnant and breastfeeding women, people over 65 years old and people with darker skin tones are groups at higher risk of low vitamin D (1).

Importance Of Vitamin D For Athletes

Vitamin D is essential for athletes as it effects bone density, bone mass, muscle strength and immune system which could have major implications on an athletes overall physical performance (6).

Stress fractures are becoming too common in the runners which could be due to not fuelling their bodies and over training. Not only does vitamin D assist in growth and maintenance of bone but it also regulated electrolyte metabolism, protein synthesis, gene expression and immune function (6). These functions are essential for all individuals but especially for elite and recreational athletes.

Athletes who are prone to musculoskeletal pain or who have stress fractures or who are ill frequently may have a vitamin D deficiency. Increasing vitamin D levels can reduce inflammation, pain and increase muscle protein synthesis (MPS), strength, exercise capacity and physical performance (8).

Vitamin D deficiency prevalence in athletes is thought to be over 50% overall and has been found even higher during winter and spring (9). Athletes who train and compete indoors are avoiding the sun exposure and are at a greater risk for vitamin D deficiency.

Low vitamin D intake in some cases can cause bone or joint injury or muscle weakness (10). To prevent this from happening, optimal vitamin D intake as well as calcium and phosphorus intake are extremely important for athletes (11).


(1) British Dietetic Association 2021. Vitamin D. Available at: <> [Accessed 5 January 2021].

(2) Office of Dietary Supplements. 2021. Office Of Dietary Supplements - Vitamin D. Available at: <> [Accessed 5 January 2021].

(3) NHS 2021. Vitamins And Minerals - Vitamin D. [online] Available at: <,condition%20called%20osteomalacia%20in%20adults.> [Accessed 5 January 2021].

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(5) Macdonald, H., Mavroeidi, A., Barr, R., Black, A., Fraser, W., &amp; Reid, D. (2008). Vitamin D status in postmenopausal women living at higher latitudes in the UK in relation to bone health, overweight, sunlight exposure and dietary vitamin D. Bone, 42(5), 996-1003.

(6) Ogan D, Pritchett K. Vitamin D and the athlete: risks, recommendations, and benefits. Nutrients. 2013;5(6):1856-1868. Published 2013 May 28. doi:10.3390/nu5061856

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(8) Shuler FD, Wingate MK, Moore GH, Giangarra C. Sports health benefits of vitamin d. Sports Health. 2012;4(6):496-501. doi:10.1177/1941738112461621

(9) Goolsby, M., &amp; Boniquit, N. (2016). Bone Health in Athletes. Sports Health: A Multidisciplinary Approach, 9(2),108-117.

(10) Potgieter, S. Sport nutrition: A review of the latest guidelines for exercise and sport nutrition from the American College of Sport Nutrition, the International Olympic Committee and the International Society for Sports Nutrition. S. Afr. J. Clin. Nutr. 2013, 26, 6–16.

(11) Ercan S (2018) The Status of Micronutrient

Elements in Adolescent Athletes: A Gastronomy City Example. / Adolesan Sporcularda Mikrobesin Öğelerinin Durumu: Bir Gastronomi Şehri Örneği. Spor Hekimligi Dergisi/Turkish Journal of Sports Medicine 53, 182-194.

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