Niacin, or vitamin B3 is added to white bread and cereals, and present in high doses in some supplements. But do we need this fortification?
As mentioned in the Vitamins and minerals section (page 111), vitamin B3, or niacin, is an essential micronutrient that supports the nervous system and is required for good skin. Deficiencies can result in weakness, loss of appetite, dermatitis, diarrhoea and, at the extreme, dementia. It is found in wholegrain products, peanuts, sesame seeds, fish and most meat.
You may have noticed that it is added to many breakfast cereals, and it is also added by law to white flour (and hence white bread) in the UK, as in the 1950s the government reacted to the new enthusiasm for white bread, which lacks some of the nutrients of the wholegrain equivalent. To be honest, the level in flour and bread isn't enough to make a huge difference - and these days few of us in developed countries lack niacin.
However, there is a concern about over-consumption of niacin in supplements. A young child, for instance, being given a multivitamin on top of a normal diet can end up with around 600% of their RNI (the amount that is enough, or more than enough for 97% of the population). And an adult taking a high dose of, say, brewer's yeast, could be on 1,000% of their RNI from that alone.
The reason this is a worry is that B3 is one of the vitamins that can cause problems in excess. At high levels it can cause skin flushes, rashes and at the extreme stomach bleeds and an increased risk of diabetes. Serious problems over and above the flushes are only likely to be caused by consumption well over 1,000% of RNI, but even so, this is a good example where unnecessary supplements can actually have a negative effect. And we particularly need to be careful with young children.
Vitamins aren't sweets and care needs to be taken with dosing, bearing in mind that most of us get a lot of vitamins already in our diet.