Long life, freedom from disease and illness, and the energy, vitality and well-being to achieve our goals is what our nation needs. This goal - good health - is one that Scotland is working hard at. With its five ancient universities and world renowned medical schools, it is a paradox that Scotland is now languishing near the bottom of the European league on so many health indicators. Vitamin D is a real contender among the newer potential interventions for improving individual and public health, and The Times is to be applauded for bringing this to our attention.

My parents bought me from sunny Punjab to foggy Gorbals, in Glasgow, in December 1955. Growing up in the 1950s and 1960s, I had to endure a daily spoonful of cod liver oil, which everyone, especially my mother, knew was essential to good health, and particularly growing bones. We knew this was important because of the vitamin D. I continued this policy with my children. We take cod liver oil capsules for six months beginning in October, until the sun and heat returns (sometimes) in April.

It has long been established that shortage of vitamin D is particularly prevalent in Scotland, and much more so in those with a dark skin, particularly in South Asians (Indian, Pakistani and Bangladeshi people). The childhood bone disease caused by severe deficiency of vitamin D used to be known as Glasgow rickets, and then in the 1970s and 1980s as Asian rickets. Many guidelines were written following this research, but a campaign to have chapati flour fortified with vitamin D failed. There is rock-solid evidence that vitamin D is essential to bone health. I have no doubt we should be implementing our existing guidelines on vitamin D vigorously. This work needs to be restarted today.

More controversial is the idea that vitamin D might be very important to a wider range of diseases, including diabetes and related states that impair glucose metabolism, which has been around for a very long time. Even more importantly, it might also be related to cardiovascular diseases (including heart attacks and strokes), cancers and life expectancy. The evidence we have indicates that we would need to boost vitamin D levels very greatly to achieve these potential benefits. In Scotland that would mean tripling the blood levels of vitamin D in many people, and a five to sevenfold increase in a few people. To put this into perspective, I would need to increase my cod liver oil from one capsule to somewhere between five and ten daily, to get that level (of course, I would seek a different formulation). The evidence for the benefits of high vitamin D levels are mounting, as Oliver Gillie's recent report, and the Times coverage have shown. So, what should we do in Scotland? In my view, it would be premature to take steps to double, triple or quadruple the Scottish population's vitamin D levels through dietary supplementation without the research that epidemiology and public health scientists have established as the minimum before implementing any national health programme.

We need to find out how much vitamin D, and in what format it needs to be taken; whether the Scottish population will actually accept such an intervention; how the changes will be delivered; and we need to document the long-term effects. Every powerful remedy has powerful side-effects. The benefits may be greater, lesser, or much the same in Scotland as elsewhere. Only time will tell. In my view, the best way forward is a large-scale, Scotland-wide trial of the effectiveness and costs of vitamin D supplementation. Fortunately, we have been planning this very study for the past 15 months, with many vitamin D experts and enthusiasts (including Oliver Gillie and Dr Helga Rhein). Scotland is extremely well placed to do this kind of work. With such data behind us, the case for fortification of core foods can be made that much more easily; the supplementation of essential substances may not only fail to yield benefits, but can do serious harm.

As to exposure to sunshine, it is largely a personal choice. If you do not get burnt, and you do not overdo it (both of which will increase your risk of skin cancer), you should, in my view, taken every opportunity to soak up the sun. I am writing this article at 4am in Rio de Janeiro, and in a few hours I hope to boost my vitamin D levels on Copacabana Beach. Sadly, the weather forecast here reminds me of the daily forecast in Scotland! It looks like cod liver oil capsules will be needed again on the first day of October.

Professor Bhopal is Alexander Bruce and John Usher Professor of Public Health at the University of Edinburgh, and honorary consultant in public health at Lothian Health Board