How are national dietary guidelines researched and set?

SACN stands for Scientific Advisory Committee on Nutrition, which is a government advisory body, and its remit is to advise government ministers on any issues relating to the diets and the nutritional status of the UK population. Mainly, the committee itself, of which I am a member, will horizon scan for emerging concerns around a particular nutrient or energy in the diet. Occasionally, government ministers will respond to a particular paper in the scientific press and ask us to look closely at a potentially important nutritional issue. A contemporary example of an issue that we’ve considered recently relates to vitamin D.

Vitamin D is an unusual vitamin in that technically we should not need it in the diet, and it acts more like a hormone than a vitamin, such as vitamin C. We know that we can synthesise vitamin D in our skin through the action of UVB in sunlight, and we can also obtain it from the diet. The fact is that there are very few dietary sources of vitamin D, which is why there is a need to be in the sunshine in the summer months so that we can make vitamin D. And for many people, that will be adequate to make enough vitamin D for the rest of the year.

But people who don’t go out into the sunlight, or cover themselves up, or use a very high factor sunscreen, are much more reliant on dietary sources of vitamin D. Until recently, there has been no dietary reference value for vitamin D for anybody in the UK between the age of 4 and 65 years of age, because it was assumed that enough vitamin D was synthesised in our skin in the summer months to be adequate for the rest of the year. But over the last few years, it was realised that this was simply not true. Furthermore, many adverse health outcomes have been associated with a low vitamin D status.

And so it was decided that we should carry out a complete review of the dietary requirement for vitamin D for the UK population. So we first of all had to develop a committee, mainly of scientists who are experts in one aspect of vitamin D, and we had a lay person and a member from industry. And we identified those public health issues that had been associated in the literature with a poor vitamin D status. And we slowly and methodically went through all the evidence linking vitamin D with an adverse health outcome. For example, a cancer, or cardiovascular disease, or musculoskeletal health. We agreed that the evidence supporting a link between vitamin D intake and musculoskeletal health was the strongest.

So this was the health outcome that we then based our consideration of the dietary reference value. The first thing we had to do was to identify a blood concentration of vitamin D below which we agreed there was an increased risk of poor musculoskeletal health. Then we had to relate this to a dietary intake. So we looked at the evidence using randomised controlled trials that would help us link this threshold for blood concentration of vitamin D with a particular dietary intake of vitamin D.

And we looked at evidence from studies in young people, in adults, and in older people - importantly carried out in a part of the UK in the winter so that we were looking at the relationship when there was no significant synthesis of vitamin D from sunlight. And using those data, we agreed that all the UK population required an intake of 10 micrograms of vitamin D daily, or approximately daily, to achieve this blood concentration of vitamin D all the year round. First of all, we produced this report, this huge report. But the key is in the final page in which we make the recommendations. We made the recommendations to government health ministers.

So we’ve carried out the scientific part of the exercise, we’ve established new dietary reference values for vitamin D for all age groups in the UK population, and we have made recommendations around how much vitamin D to take to keep a healthy blood level. And it is now up to the health ministers in the UK government to decide how to use those recommendations. So this is a nice example of the way the science is used to establish dietary reference values and how recommendations are made to government.

And how then the government will need to consider what the implications are around, for example, the need to put more vitamin D in food, or to make it easier and cheaper to buy vitamin D supplements.