More on Vitamin D

What does it do? Vitamin D is present in at least 38% tissues in the body - and probably present in all of them. It is known to play an important role in the immune system, the heart and blood vessels, in the pancreas, in muscle development and strength and in brain development. A study in 2012 found it has a direct influence on 229 genes involved in disease, especially those associated with multiple sclerosis, Crohn's disease and type 1 diabetes. It plays a crucial role in activating our immune defences by triggering and arming the body's T cells, which seek out and destroy invading bacteria and viruses.

• Colds and Flu: Vitamin D supplements reduced the incidence of colds and flu by 70% over 3 years in US Afro-Caribbeans, who are more vulnerable to deficiency because of their dark skin.
• Heart Disease: Multi-study analysis indicated that middle-aged and elderly people with high levels of vitamin D in theit blood had a 43% reduced risk of heart disease and diabetes. 
• Diabetes: Vitamin D supplements given to babies in Finland reduced their risk of type 1 diabetes by 80%.
• Multiple Sclerosis: There is some evidence that vitamin D deficiency in pregnancy and in the early years of life may play a role in the development of MS.
• Cancer: A growing number of research studies link low vitamin D levels with an increased risk of breast, bowel and prostate cancer. Another study found that melanoma (skin cancer) patients with the lowest vitamin D levels were 30% more likely to relapse after treatment than those with the highest levels.
• Pregnancy: A US study found that pregnant women taking very high daily doses of vitamin D were 50% less likely to experience pre-term labour, pre-eclampsia, gestational diabetes and infections than those on the lowest dose.
• Joint health: A new study suggests living in a sunnier climate may reduce the risk of rheumatoid arthritis.
• Asthma and Autism: Low levels of vitamin D in pregnancy have been linked with autism, and asthmatic children with low levels seem to suffer more severely.

Who is at risk? The vast majority of the UK population and especially, pregnant and breast feeding mothers, children under four, people over 64, and those with darker skin or whose skin is not exposed to the sun very much. Why? People with darker skin need more time in the sun to make the same amount of vitamin D. Older people have a reduced ability to make vitamin D. People who are obese are also at greater risk as vitamin D is fat soluble, so will be stored in the fat cells, with very little released into the bloodstream where it is needed.

Food Fortification Although vitamin D is found in some foods (oily fish, eggs, fortified margarines) we cannot get enough to from dietary sources alone. Unlike other countries, the UK has no recommended daily intake level for people aged 4 to 64 (2011). Some scientists feel we need to fortify certain foodstuffs with vitamin D - suggested foods are milk, orange juice and cereals. Vitamin D levels can be topped by supplements in tablet or liquid form.

Good Housekeeping issues August 2011, June 2013