Vitamin D (Calciferol)
Vitamin D is vital for the regulation of blood levels of calcium and phosphorus, required for the maintenance of strong and healthy bones, teeth and muscles. It also plays an important role in activating the immune system, and research has shown that flu incidence may decrease when Vitamin D3 supplements are taken, while deficiency has been linked to increased risk or severity of viral infections, including HIV.
According to the National Institute for Healthcare and Excellence, around 20% of the UK population has low vitamin D status. The European Food Safety Authority recommends an intake of 15μg per day of Vitamin D for everyone over the age of one year.
The synthesis of vitamin D is dependent upon the presence of ultraviolet B (UVB) light and subsequent activation in liver and in kidney. Around 90% of our vitamin D intake is believed to be derived from sunlight. During spring and summer most individuals should be able to obtain adequate Vitamin D from exposure to the sun. Thirty minutes twice a week is considered to be sufficient. The skin will reach an equilibrium where the vitamin degrades as quickly as it is created, so overdose is not possible from UV exposure. The darker the skin and the weaker the sun, the more minutes of exposure are needed. It is important to remember to cover up or protect the skin when out in the sun for prolonged periods to reduce the risk of skin damage and skin cancer.
During autumn and winter, when the sun is less strong, additional dietary sources of the vitamin, or a supplement, are required. Public Health England recommends that everyone should consider taking a daily supplement containing 10 µg of vitamin D during autumn and winter because of inadequate sunlight for vitamin D synthesis.
Some people are unable to obtain sufficient Vitamin D from the sun, for example, the old and frail and housebound and those who cover up for religious or cultural reasons. The body’s ability to synthesise Vitamin D declines with age. Dark-skinned individuals of African, Afro-Caribbean and South Asian heritage are also at risk because they may be less efficient at making vitamin D because more melanin in the skin hinders its synthesis. In those cases a Vitamin D supplement would be of benefit.
There are several natural sources of Vitamin D. D2 (ergocalciferol) is found in fungi and yeasts while D3 (cholecalciferol) is found in animals. D2 and D3 are known collectively as calciferol. The best dietary sources include oily fish such as herring, mackerel and salmon, oysters, red meat, liver, egg yolk, cottage cheese, wild mushrooms and fortified spreads or breakfast cereals. Frying, boiling and baking food can deplete up to 30% of the vitamin.
Research has shown that pregnant women who take adequate amounts of vitamin D may reduce their risk of risk of pre-eclampsia, and giving birth to undersized babies with a poor rate of growth. Pregnant or breastfeeding women should consult a doctor before taking a vitamin D supplement.
Inadequate Vitamin D can lead to bone deformities such as rickets in children and osteomalacia in adults. Rickets used to be a major public health problem, but an increase in the proportion of animal protein in our diets and infant vitamin supplements have largely consigned it to history in the West. Characteristics of osteomalacia in adults are softening of the bones, spine deformities, bowing of the legs and an increased risk of stress fractures due to reduced calcium absorption and increased calcium loss from the bones. Low bone mineral density may result in osteoporosis. Muscle pain, weakness and fatigue may also be features.
A recent study has identified a possible link between low levels of Vitamin D and poor sleep quality. It has also been concluded that low levels of the vitamin are associated with low mood and depression. Seasonal Affective Disorder may occur when lower levels of vitamin D affect the concentration of serotonin, a neurotransmitter that helps regulate mood, in the brain.
A five-year study in the US found that women with low Vitamin D status were more prone to weight gain than those with adequate levels. Another study showed that the amount of circulating vitamin D was improved by weight loss, indicating that fat mass may be inversely associated with blood levels of vitamin D.
Vitamin D deficiency can both be a cause and result of gastrointestinal problems. Conditions affecting fat absorption also affect the absorption of Vitamin D which is fat-soluble. A study conducted by the University of Sheffield suggested that those suffering from irritable bowel syndrome were often deficient in the vitamin. Crohn’s disease and ulcerative colitis are also associated with low levels of vitamin D.
Taking too many vitamin D supplements over a long period of time can cause too much calcium to build up in the body resulting in a condition known as hypercalcaemia, characterised by nausea, increased urination and thirst. If left untreated, excess calcium deposits may cause damage to the kidneys, liver and heart. Certain medical conditions, such as primary hyperparathyroidism, can cause sensitivity to vitamin D leading to the development of hypercalcemia.
NB: Always consult a health professional before taking supplements