Reduced folate status is common and increases disease risk. It can be corrected by daily ingestion of supplements or fortification.

The natural folates are chemically unstable and poorly bioavailable in contrast to the chemical form, folic acid. Consequently most people, even those on good diets, have less than optimal nutrition with respect to this vitamin. Increased risks associated with deficiency include neural tube defects (NTDs) (proven), ischaemic heart disease and stroke (probable), certain cancers and decline in cognitive function (possible). Supplements of folic acid at the population reference intake (400 microg/d) completely normalizes all of these risks. Such levels are safe as judged by decades of use in wide sectors of the population. The main drawback of supplements is with respect to their effectiveness in preventing NTDs. They must be taken periconceptionally and before most women realise that they are pregnant. No more than one fifth of women take supplements effectively, largely due to the fact that over half of pregnancies are unplanned. This has led to the alternative of mandatory fortification of flour with folic acid in the USA and Canada. The level for such fortification is suboptimal for NTD prevention, because of fear of overexposure in the elderly. Thus even fortified communities require advice to take supplements for optimum NTD prevention.