Think you need vitamin D supplements?

As vitamins go, vitamin D is quite a trendy one at the moment. Stick 'Vitamin D Deficiency' into Google and within seconds over 16m hits appear. Books have been written about it and articles published about it, yet its celebrity status was ultimately sealed when Gwyneth Paltrow revealed that she too was deficient in it. Given that at the moment it is hard to move without hearing about this nutritional supplement, or that 'super-food'… what is the deal with vitamin D?

Vitamin D is vital to ensure we have healthy and strong bones. Low levels of vitamin D are known to cause significant bone disease, both in adults and children. Rickets, which is thankfully vanishingly rare in this country, is the childhood bone disease cause by vitamin D deficiency. However, over recent years there has been much interest in potential links between low vitamin D levels and a plethora of seemingly unrelated conditions, such as cancer, heart disease, diabetes, dementia, multiple sclerosis and autoimmune diseases to name but a few. Although the scientific community is beavering away hard, this is all very much still in the research stage and no formal associations, to date, have been made.

Symptoms of low vitamin D are quite vague in the initial stages. Adults typically complain of muscle and joint aches, fatigue and feeling generally below par. Checking vitamin D status is easily done via a blood test and can be carried out at most GP surgeries.

Vitamin D is present in few foods. Oily fish, liver and eggs can provide us with some vitamin D, but 90% of our body stores come from exposure to sunlight. It is estimated that for people with fair skin, 20-30 minutes of sun exposure two to three times per week is sufficient to maintain healthy levels of vitamin D. People with darker skins may require between two to 10 times this level of exposure to preserve adequate vitamin D stores. Don't forget that you will also only do the job properly if you actually let sun rays fall on to uncovered skin. Sitting in the shade or being smothered in suntan lotion unfortunately will do nothing for your vitamin D. In addition, due to the UK's northerly location, it is generally accepted that between the months of October to April it is nigh on impossible to maintain vitamin D levels, as there isn't enough UV light filtering down to our chilly Isle.

Does this matter? We know that extremely low vitamin D concentrations can lead to serious bone disease and should be promptly treated with prescribed supplements. However, there is a grey area between totally normal vitamin D levels and true deficiency. This is often categorised as being a 'sufficient' or 'sub-optimal' level, and as yet we don't fully understand the long-term significance of this.

Currently the jury is still out as to the best strategy in dealing with moderately low vitamin D levels, especially as in the winter months it may affect the vast majority of us. Back in 2012 the Department of Health released advice suggesting that those most vulnerable should take vitamin supplements prophylactically; this includes children under five, pregnant and breast-feeding mothers and adults over 65 with limited sun exposure. Whether the rest of us need to do anything other than pop into the garden from time to time and eat a few extra sardines, only time will tell.

Dr Jessica Garner is a GP and health blogger. Visit her blog here.