A few quick notes about Vitamin D, a fat soluble steroid vitamin of which there are 5 forms but the major ones are D2- cholecalciferol and D3- ergocalciferol. It is obtained from the diet and also from sun -exposure (made from cholesterol) In the liver, it is converted to calcidiol (this is what is measured in the blood), part of this goes to kidney where its converted to calcitriol (the biologically active form of vitamin D). Calcitriol is a hormone that regulates calcium and phosphate, promoting bone growth and remodelling.
The current recommendation of 600IU is too low to achieve adequate levels and ideally 1000-4000IU daily would be the recommendation. A recent US study suggested a level of 100nmol/l would be ideal.
Sources of Vitamin D
Oily fish, cod liver oil, eggs, fortified milk, cheese, fortified cereals, liver, alfalfa, mushrooms (In Australia, UV treated mushrooms are now available)
Vitamin D and your health
Bone health– Its role in bone health is well known (prevention of osteoporosis and rickets) as it has a crucial role in calcium and phosphorus metabolism but vitamin D has much more of a varied role than previously thought.
Heart disease and stroke– Low levels have been linked to cardiovascular disease and stroke (Honolulu heart program, a study published in the American Heart Association found that vitamin D is an independent risk factor for 34 year incidence of all stroke for Japanese-American men)
A 2007 study (American Journal of Clinical Nutrition) involving 63 overweight or obese women were given 400IU Vit D and 1200mg Calcium and over a 15 week period there were reduced cholesterol levels in this group compared with the placebo group.
Weight– many studies have found a correlation between low vitamin D and weight gain.
A 2010 study (American Journal of Clinical Nutrition) involving 126 women who were followed for 6m found that low levels decreased likelihood of weight loss.
2007 study (Archives of Internal Medicine)- 36,282 post-menopausal women were given either 400IU Vit D with 1000mg Calcium OR placebo. They were followed for 3 years and the treated group were 11% less likely to gain weight.
Immune system– a very important immune system regulator. Low levels are linked to the common cold and flu– it is thought that increased illness in winter could be due to the low levels as a result of reduced sun exposure. A 2009 study (Archives on Internal Medicine) found that low levels were linked to increased frequency of the common cold and flu (esp if they already have asthma and emphysema).
Rheumatoid Arthritis– A study published in the Medical Journal of Arthritis and Rheumatism showed that women with high levels of vitamin D had 30% less likelihood of developing rheumatoid arthritis.
Cancer– A Study by CTCA (Cancer Treatment Centre of America) found Vitamin D deficiency was prevalent in cancer patients and there is increasing amount of evidence that vitamin D has a protective role in cancer.
Cognitive function– a 2009 study (Journal of Neurology, Neurosurgery and Psychiatry) involving 3000 men between 40 and 79 showed that those with lower levels had poorer scores (mental agility was tested using various tests)
Multiple sclerosis– low levels may be linked to developing MS which is much less common as you get nearer the tropics where theres more sunlight.