Vitamin D is responsible for the uptake and absorption of calcium and phosphates in the intestine. It is therefore important for bone production and a deficiency can lead to a condition called rickets (weak bones and chronic pain).
Although called a Vitamin it is not one in the true sense because the body is able to synthesise it from cholesterol via the action of sunlight. However it was treated as a Vitamin when discovered because of the difficulty in the body making and storing sufficient quantities (it only lasts around 60 days when stored).
What does it do?
As well as being important for bones, it is also needed for cell growth, nerve, muscle and immue function. It helps prevent osteoporosis, rickets in children and osteomalacia in adults (muscle and bone weakness and bone pain).
Other studies have found it helps with:
- Diabetes : Australian research has shown it may reduce the risk by as much as 57%.
- Allergies: Vitamin D is thought to have an anti-inflammatory effect on the body. A US study found children low in Vitamin D were twice as likely to have allergies.
- Auto immune disorders: Studies in the US suggest vitamin D deficiency may increase the risk of Lupus, rheumatoid arthritis and Crohns disease.
- Heart disease: Patients who increase their levels of Vitamin D have lower rates of heart failure, cariovascular disease and high blood pressure.
- Colds: Research shows Vitamin D boosts immunity from colds and flu.
Why aren’t we getting enough?
It can be hard to get enough sunshine in the UK, especially in the winter. Plus the widespread use of sunscreen has limited the sun that does reach our skin. Our diets also may not contain enough of the foods which could supplement our levels such as oily fish, milk, eggs, tofu and wholegrain cereal. Some foods are fortified with vitamin D such as fat spreads, cereals and powdered milk.
It’s ironic that one of the best sources of Vitamin D is Cod liver oil, so our parents and grandparents knew a thing or two about supplements!
There are 2 types of Vitamin D available, D2 and D3. It is thought that D3 is the better supplement to take as this is what the body naturally produces from sunlight. Some people are more vulnerable to Vitamin D deficiency than others, these include:
- all pregnant and breastfeeding women
- babies and children younger than five
- older people aged 65 years and over
- people who are not exposed to much sun, such as people who cover up their skin when outdoors or those who are housebound or confined indoors for long periods
- people who have darker skin such as people of African, African-Caribbean and South Asian origin
The Science bit!
Hypovitaminosis D is a significant public health concern.3–5 In a study of healthy adolescents, Gordon et al5 found that 24.1% were vitamin D deficient and 42.0% were vitamin D insufficient. LeBoff et al4 found an association between hip fractures in older women and lower levels of 25-hydroxyvitamin D. Vitamin D deficiency may contribute to metabolic syndrome.6,7 Vitamin D seems to play a protective role against breast, prostate, and colon cancer.8Animal experiments link vitamin D deficiency to abnormal brain development. The broad spectrum of effects from suboptimal levels of vitamin D reflect its varied functions. Vitamin D plays important roles in bone health and mineral homeostasis, immune modulation, muscle function, nervous system function, control of the renin-angiotensin system, control of insulin secretion, skin function, regulation of apoptosis, and regulation of cell growth.
Cod liver oil contains both vitamin D and omega-3 LCPUFAs.2 Individuals at higher risk for vitamin D deficiency may wish to consider substituting cod liver oil for fish oil supplementation.
Oh R. Practical applications of fish oil (omega-3 fatty acids) in primary care. J Am Board Fam Pract 2005; 18: 28–36.
Linday LA, Dolitsky JN, Shindledecker RD. Nutritional supplements as adjunctive therapy for children with chronic/recurrent sinusitis: pilot research. Int J Pediatr Otorhinolaryngol 2004; 68: 785–93.
Thomas MK, Demay MB. Vitamin D deficiency and disorders of vitamin D metabolism. Endocrinol Metab Clin North Am 2000; 29: 611–27, viii.
LeBoff MS, Kohlmeier L, Hurwitz S, et al. Occult vitamin D deficiency in postmenopausal US women with acute hip fracture. JAMA 1999; 281:1505–11
Gordon CM, DePeter KC, Feldman HA, et al. Prevalence of vitamin D deficiency among healthy adolescents. Arch Pediatr Adolesc Med 2004;158: 531–Ford ES, Ajani UA, McGuire LC, Liu S. Concentrations of serum vitamin D and the metabolic syndrome among U.S. adults. Diabetes Care 2005