From the health of your immune system to the prevention of many diseases including cancer, diabetes, Alzheimer's, depression, and even protecting against influenza, vitamin D is now seen as one of the most critical nutrients for overall health.

But it is also one of those most likely to be deficient - especially during the winter months when production of this "sunshine vitamin" is at its lowest for many people. In fact, a recent clinical review found an alarming rise in the cases of rickets among UK children, thought to be because of lack of sunlight exposure, especially during winter when much of the UK does not get enough ultraviolet light of the appropriate wavelength for the body to make vitamin D in the skin. Rickets is a bone disease caused by a lack of vitamin D, which can lead to deformities, stunted growth and general ill-health.

Vitamin D is largely made by the skin through exposure to sunlight, but can also be found in certain foods including oily fish and eggs.

Here is a selection of some recent findings of the health benefits this remarkable vitamin is associated with.

Vitamin D Protects the Immune System

vitamin D is being called "nature's antibiotic", after recent discoveries found that it helps serve as the first line of defense in your immune response against minor wounds, cuts, and both bacterial and viral infections.

Scientists found that it induces the "expression" of cathelicidin, an antimicrobial peptide gene, which could explain its multiple roles in proper immune function. Vitamin D plays an important role in activating the immune system, and can help control autoimmune diseases such as multiple sclerosis, psoriasis and rheumatoid arthritis.

Studies also show a link between vitamin D deficiency and increased rates of respiratory infection and influenza, and it has been hypothesized that flu epidemics may be the result of vitamin D deficiency.

Higher levels of a protein linked to vitamin D have also been associated with reduced infections and longer survival of dialysis patients.

Research paper details:

Gombart AF. The vitamin D-antimicrobial peptide pathway and its role in protection against infection. Future Microbiology, November 2009, Vol. 4, No. 9, Pages 1151-1165.

Higher vitamin D Levels Linked to Lower cancer Risk

A recent study found that those with higher blood levels of vitamin D were at 40 per cent lower risk of developing colon cancer than those with low levels.

Scientists looked at vitamin D quantities in 1,248 people with bowel cancer and 1,248 controls in the largest ever study of the subject. Participants completed detailed dietary and lifestyle questionnaires and blood samples were collected. The subjects were then tracked for several years, during which time 1,248 cases of colorectal cancer were diagnosed and these were matched to 1,248 healthy controls.

Participants with the highest levels of blood vitamin D concentration had a nearly 40% decrease in colorectal cancer risk when compared to those with the lowest levels.

The authors said that with respect to colorectal cancer protection, it is still unclear whether inducing higher blood vitamin D concentration by supplementation is better than a balanced diet combined with regular and moderate exposure to outdoor sunlight.

Research Paper Details:

Jenab et al. Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations:a nested case-control study. BMJ, 2010; 340 (Jan21 3): b5500.

Vitamin D Prevents Diabetes

In a report published recently, scientists found that vitamin D supplementation among South Asian women decreased their risk of developing diabetes. The women were all diagnosed with insulin resistance syndrome, also known as metabolic syndrome. This condition, which is linked to an increased risk of both diabetes and heart disease, describes a cluster of health conditions that includes high blood sugar levels, high triglycerides, and too much fat around the waist.

After six months of taking either 4,000 IU of vitamin D3 daily or a placebo, the results showed significant improvements in the vitamin D group. Specifically, their insulin resistance dramatically improved with a decrease in their fasting insulin levels. This slashed the risk they would go on to develop diabetes.

Previous research also backs up this theory. Indian scientists found that even a short-term large dose of vitamin D3 supplementation had a positive impact on insulin sensitivity in 71 apparently healthy, middle-aged men with central obesity associated with the pre-diabetes metabolic syndrome. Taking vitamin D3 improved their postprandial (after a meal) insulin sensitivity, lowering their risk of developing diabetes later in life.

Research paper details:

von Hurst PR, Stonehouse W, Coad J. Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient - a randomised, placebo-controlled trial. Br J Nutr. 2009 Sep 28:1-7.

Nagpal J, Pande JN, Bhartia A. A double-blind, randomized, placebo-controlled trial of the short-term effect of vitamin D3 supplementation on insulin sensitivity in apparently healthy, middle-aged, centrally obese men. Diabet Med. 2009 Jan;26(1):19-27.