Vitamin D is a fat soluble vitamin also known as Cholecalciferol. It is often referred to as the ‘sunshine vitamin’ due to the fact that it can be made in the body by the action of sunlight on the skin. For this reason it is also considered as a hormone. Dietary sources include oily fish, milk and dairy products. In terms of Recommended Daily Amounts (RDA), in July 2016 Public Health England published guidelines for vitamin D and the recommendations are as follows; Babies from birth to 1 year: 8.5-10µg all year round. Children over 1 year and adults: 10 µg in the winter months. Pregnant and breastfeeding women and population groups at risk of vitamin D deficiency (those with minimal exposure to sunshine and those from minority ethnic groups with dark skin): 10 µg /day all year round.
Vitamin D is necessary for the absorption of calcium and for bone growth. It also plays a role in regulating the immune system and is believed to exert many anticancer properties.
Severe vitamin D deficiency is associated with a condition known as Ricketts, a condition which is characterised by softening of the bones and skull, bowing of the legs, spinal curvature and increased joint size. This is now a rare disease however mild vitamin D deficiencies can be common in the UK due to lack of sunlight, especially during the winter months. Deficiency is common in the elderly due to immobility and lack of sunlight. Deficiency has been linked to the development of heart disease, osteoporosis and diabetes (Balch, 2010). Vitamin D deficiency has been associated with increased risk of common cancers, autoimmune diseases, hypertension, and infectious diseases (Holick, 2008). A deficiency has also been linked with fatigue, low mood, poor immunity and general aches and pains.
Asthma-Research suggests that Vitamin D may play a role in the prevention of asthma. Animal models and studies in human foetal tissues show that vitamin D is involved in foetal lung growth and maturation. From these findings it has been suggested that improving vitamin D is proving promising in the prevention of asthma, in decreasing exacerbations of disease, and in treating steroid resistance (1).
Depression-There is evidence to suggest there is also a link between Vitamin D deficiency and depression. One controlled study involving 31, 424 participants found that vitamin D levels were lower in those suffering with depression, demonstrating the potential association between the two (2).
Male hormones-Early findings have also highlighted a potential association with lowered testosterone in males and vitamin D deficiency. A randomized controlled study involving 200 heavy weight males revealed vitamin D supplementation increased levels of testosterone in these subjects (3).
Cancer- In relation to the association of Vitamin D and cancer, a cross-sectional study of 3,121 adults aged 50 years who underwent a colonoscopy found that 10% had at least one advanced cancerous lesion however those with the highest vitamin D intakes (>645 IU/day) had a significantly lower risk of these lesions (4).
Osteoporosis and Bone Health- Vitamin D contributes to normal absorption/ utilisation of calcium levels and phosphorus, contributes to normal blood calcium levels and contributes to the maintenance of normal bones. These three factors in combination make vitamin D one of the most important nutrients for maintaining the correct structure and function of bone. It is thought to help increase the uptake of calcium from food and reduce calcium loss in the urine. A deficiency could therefore interfere with processes and inhibit the formation of normal bone. This may also be important in cases of bone fractures and breaks, as Vitamin D deficiency may inhibit the repair process.
Healthy teeth- Vitamin D contributes to the maintenance of normal teeth. This implies that a deficiency may lead to poor health of the teeth, especially when they are forming and growing in children.
Because Vitamin D is stored in the body it does have the potential to cause toxicity if taken in high doses. Toxicity may be associated with symptoms such as anorexia, weight loss, polyuria, and heart arrhythmias. High levels of vitamin D have also been shown to cause calcium to deposit in internal organs and the formation of kidney stones which can lead to serious complications. The Tolerable Upper Intake Levels for adults in the UK is 4,000IU.