Vitamin D refers to two biologically inactive precursors: D3, also known as cholecalciferol (made from cholesterol), and D2, also known as ergocalciferol. Vitamin D is the only nutrient that can actually be synthesised by the human body, which technically means it is not a vitamin. The synthesising of vitamin D in the body can be achieved through contact with solar ultraviolet B radiation emitted by the sun. Without the presence of this solar radiation, the only way to get vitamin D is through diet - hence, it is still classified as a "vitamin."
It is becoming increasingly common to find low levels of vitamin D in Western populations. Vitamin D uptake from the sun is not affected so much by seasonal changes, but by how much time people spend in the sun. People require between 70nmol/L to 100nmol/L of vitamin D and in winter, when people spend less time outdoors, it is difficult to achieve these levels. Furthermore, current sun avoidance advice, combined with the dietary habits of the general population make the situation much worse - the average level in adults is around 25nmol/L, not even half the recommended level. Populations particularly at risk are seniors and infants, but also any person spending too much time inside.
In addition to vitamin D obtained through UVB exposure to the sun, this vitamin can be found in foods such as eggs, butter and fortified milk, with the highest levels found in fish. Remember, we evolved as fisher-hunter gatherers and fish used to be an essential part of our nutrition. Vitamin D can also be provided by supplements. Numerous studies have concluded that sensible sun exposure and supplementation are the most effective ways of increasing vitamin D levels.
Once in the body, vitamin D is either stored in the body's fat adipocytes or enters the liver. The vitamin D gets broken down in the kidneys for the regulation of calcium and dozens of metabolic functions. The broken-down vitamin D then interacts with vitamin D receptors in the small intestine and on osteoblasts to regulate calcium and phosphorous metabolism. It not only assists calcium uptake in the bones, but also works as an immunity modulator. It continues to be metabolised in various tissues and cells for regulating cellular proliferation and differentiation, as well as in the functioning of the immune system and macrophages. In addition, circulating concentrations of the broken-down vitamin D may help increase insulin production and alter fat metabolism.
Deficiencies in vitamin D have been linked with a range of problems with the musculoskeletal system including low bone and muscle problems, as well as cardiovascular disease, diabetes and metabolic syndrome, cancer and impacts on the immune system, Parkinson's Disease, asthma, pain, and pre eclampsia.
Low levels of vitamin D can reduce the amount of calcium uptake in the bones which, over time, can lead to a loss in bone density. Pregnant women with vitamin D deficiency have been found to give birth to children who are at greater risk of being unable to store calcium in their bones, reducing their bone density and increasing the risk of bone fractures. In addition, these children experience higher level of dental caries. Low vitamin D in children will prevent them from reaching their bone mineral density and therefore increase their risk of osteoporosis and fracture later in life. In a study of 206 pregnant women during their second trimester, researchers reported that only 10.5 per cent of the women had adequate levels of vitamin D.
In a study of 23,423 would-be first time mothers, the risk of pre-eclampsia was 27 per cent lower in women who consumed vitamin D supplements with daily doses of 10 to 15 micrograms, compared to women who did not take supplements. Pre-eclampsia, affecting two to three per cent of all pregnancies, is estimated to be responsible for about 60,000 deaths each year worldwide.
Vitamin D deficiency is inversely related to a range of diseases, including respiratory infections such as influenza. In support of these findings, clinical trials have shown that vitamin D supplementation can reduce the risk of reactivation of latent tuberculosis infection. Vitamin D (in particular, D3) stimulates neutrophils, monocytes (natural killer cells) and the epithelial cells lining the lungs, protecting them from infection. So come wintertime and flu season, get out and get a bit more sun, along with some cod liver oil.
For a longer version of this story go to www.drdingle.com
Dr Peter Dingle PhD is an environmental and nutritional toxicologist and Associate Professor in Health and the Environment at Murdoch University.
Dr Peter Dingle (PhD) has spent the past 30 years as a researcher, educator, author and advocate for a common sense approach to health and wellbeing. He has a PhD in the field of environmental toxicology and is not a medical doctor. He is Australia’s leading motivational health speaker and has 14 books in publication.