Vitamin D

Vitamin D has many functions in the body – it regulates calcium and phosphate levels which are essential for bone building and teeth. Any absence of vitamin D in the diet and rickets develops which is a bone deformity as does osteomalacia which is pain in the bone.

Recent research has strongly shown that vitamin D3 helps stave off colds and flu.

Rickets was always associated with poor nutrition in people suffering considerable poverty.  Many children growing up in Victorian slums and the rookeries developed bowed legs and curvature of the spine. The condition was thought to have been consigned to the history books in Britain when vitamin D was added to our everyday foods such as margarine and cereal back in the 1940s. Cases of rickets dropped but then the number of children admitted to hospital started to double relatively recently in the past decade from 200 in 2004-05 to 455 in 2013-14.

Photo by Graeme Weatherstone. Courtesy of FreeDigitalPhotos.net
Barbecuing Sardines. Oily fish are a great source of vitamin D. Photo by Graeme Weatherstone. Courtesy of FreeDigitalPhotos.net

When the nights begin to draw in and the opportunity to be exposed directly to sunlight means there is less opportunity for the body to manufacture its own vitamin D [25-hydroxyvitamin D [25(OH)D]. If we are out in the sun, we only need 10 to 15 minutes each day to boost our vitamin D levels. We can of course obtain small amounts eating oily fish like salmon, sardines and mackerel, eggs, fortified butter -like spreads, powdered milk and fortified breakfast cereals.  It has long been the case that vitamin D supplementation  is exceptionally important for those who do not eat eggs, milk or fish and literally cover themselves up.  Vitamin D is extremely important – it helps in to build bones,  prevents hypocalcaemic seizure and rickets,  it reduces the risk of diseases from cardiovascular to diabetes and cancer, and generally boosts our immunity.  It is really a prohormone rather than a vitamin because it carries out is functions by acting on nuclear based receptors (DeLuca, 2004).

It seems though that many of us do not have enough vitamin D in us despite the benefits. Indeed, from the evidence of a conference in 2008 on vitamin D intake, at least half the population in the USA for example are below the optimal level and 10% of children are classified as deficient in the vitamin (Brannon et al., 2008). If the serum level is below 20 nmol/l, the deficiency can lead to rickets and osteoporosis. Levels above this are less debilitating, coloured by the fact that the optimum level for everyone is not clear because it is multi-factorial. Some researchers think 60 nmol/l in the blood is too little because of the impact vitamin D has in the body.  Medics test blood serum levels, and are prescribing supplements though  to counter the deficiency.  That supplement business is worth nearly $250 million in the USA based on some 2011 figures because about 1 in 5 citizens take vitamin D in some form or other.

Recent reports have questioned whether vitamin D supplementation is worth it. A number of observational studies have highlighted how high vitamin D supplementation reduces the risk of cardiovascular disease by up to 58%, diabetes by 38% and colorectal cancer by 33%. However, clinical trials with vitamin D supplementation did not show a clear reduction in risk, even in those with low vitamin D levels to begin with. Likewise, assessment of supplementation in randomised trials found no positive effect on preventing these diseases. A very recent report suggests that vitamin D supplementation is not required for healthy adults (Autier et al., 2014). They had conducted a meta-analysis on over a hundred studies which complemented similar work on vitamin D supplementation on bone mineral density (BDM).

One of the issues on deciding on how much vitamin D is good for you, is the scarcity of intervention studies which compare supplementation with vitamin and a placebo. It is still not clear whether overdosing might be a health issue too. One study, the VITamin D and OmegA-3 triaL (VITAL) which is assessing the link between vitamin D intake and improvements to cardiovascular health suggests the pills are not needed. If serum vitamin D levels can be improved by just being briefly outdoors, say an extra 20 minutes for example to increase exposure to the sun, then we are doing ourselves a lot of good.

The Scientific Advisory Committee on Nutrition (SACN) which advises the government on nutrition is reviewing vitamin D for all population groups in the UK. This short post doesn’t do justice to the great wealth of date available and I will be adding pertinent information as it appears. I’d be interested to know others thoughts on whether they take vitamin D in whatever form, as a supplement and whether they perceive it has done them some good.

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References

Autier, P., Boniol, M., Pizot, C., Mullie, P. (2014) Vitamin D status and ill health: a systematic review. Lancet Diabetes & Endocrinology. 2(1) pp. 76-89
Brannon, P.M., Yetley, E.A., Bailey, R.L. Picciano, M.F. (2008) Overview of the conference “Vitamin D and Health in the 21st Century: An Update”  Am. J. Clin. Nutr. 88 pp. 483S-490S
DeLuca, H.F. (2004). Overview of general physiologic features and functions of vitamin D.  Amer. J. Clin. Nutr.  80 pp. 1689-1696