Food Fortification and Public Health: Folic Acid, Vitamin D, Vitamin A and Iodized Salt

At a glance

Folic acid and neural tube defects

Folic acid is the manufactured form of folate. In 1992 the US Public Health Service recommended that all women who could become pregnant get 400 micrograms (mcg) of folic acid daily to prevent neural tube defects. [2] A randomized trial in 1991 had found folic acid prevented the defects in women who had already had an affected pregnancy. [5] Because the neural tube closes very early in pregnancy and up to half of US pregnancies are unplanned, a review argued that supplement advice alone has limits as a public health program. [1]

• United States. Mandatory fortification of enriched cereal grain products began in 1998 at 140 mcg of folic acid per 100 g. [2] Studies using different methods found decreases of 19% to 32% in the overall prevalence of neural tube defects. [1] A 2015 federal report found that after an initial fall, prevalence stayed relatively stable, and estimated about 1,326 births a year without neural tube defects that would otherwise have been affected. [2]
• Other countries. A 2011 review reported declines of 19% to 55% after fortification in Canada, South Africa, Costa Rica, Chile, Argentina and Brazil, and said mandatory flour fortification rules existed in 53 countries, though often not implemented. [1]
• United Kingdom. Under rules in force from 13 December 2026, non-wholemeal wheat flour must contain 0.25 mg folic acid per 100 g, with exemptions for small mills and wholemeal flour. [6] The government expects this to prevent around 200 cases a year, a projection, not a result. [7] It says the NHS advice to take folic acid supplements before and during early pregnancy stays in place. [7]

Limits. These population results come from before-and-after surveillance, not randomized trials of fortification; a review noted that studies of effects after fortification, such as cross-sectional and ecological ones, cannot establish causation. [1] Concerns include high total intake from supplements, fortified cereals and enriched grains together [1], and that more than 1 mg a day of folic acid can mask the signs of vitamin B12 deficiency, which can damage the nervous system if missed. [8] See Folic acid fortification and unmetabolized folic acid and Folic acid and folate before and during pregnancy.

Vitamin D in milk and other foods

In the US federal standard for milk, adding vitamin D is optional; if added, each quart must contain 400 International Units. [9] Policies elsewhere differ and I did not read a source for them.

A 2025 systematic review pooled 35 randomized trials (4,965 participants) of vitamin D-fortified dairy products against unfortified ones. Serum 25-hydroxyvitamin D rose, for example by a mean 18.31 nmol/L with vitamin D3-fortified milk or milk powder (95% confidence interval 13.30 to 23.33), though results varied a lot between trials (I-squared 95%). [3] That is a blood marker. Proper evidence not found in the sources I searched (PubMed and Europe PMC for fortified milk, rickets and fortification history) for rickets or fracture outcomes from fortified foods. For background on rickets see Rickets and osteomalacia.

Vitamin A

The WHO says vitamin A deficiency is the leading cause of preventable blindness in children and raises the risk of death from infections such as diarrhoea and measles. [4] It also lists fortification of foods among its programs, and in October 2025 listed a guideline on fortifying edible oils and fats with vitamins A and D; I read only that listing, not the recommendations. [4]

A related but different intervention is vitamin A supplementation for young children in high-risk areas. A Cochrane review (2010) of 43 trials in 215,633 children found about a 24% lower risk of death from any cause (relative risk 0.76, 95% confidence interval 0.69 to 0.83) and more vomiting in the first 48 hours. [10] That review excluded fortification studies, so it should not be applied to fortified foods. [10] The WHO describes vitamin A deficiency as rarely seen in developed countries. [11] For adults, the NHS (UK) advises keeping total vitamin A from food and supplements to 1.5 mg (1,500 micrograms) a day or less. [12] See Vitamin A.

Iodized salt

Before the 1920s, 26% to 70% of children in the US "goiter belt" had visible goiter, and iodized salt first reached Michigan grocery shelves on 1 May 1924. [13] Today about 120 countries mandate iodization of food-grade salt, while in the US it is voluntary. [13] The WHO calls universal salt iodization the preferred strategy and says UNICEF estimates 66% of households worldwide have access to iodized salt. [4] An outbreak of thyrotoxicosis in adults was described in 1926 among people in the goiter belt who used iodized salt. [13] Iodine is a mineral; see Iodine for thyroid and safety information.