An estimated 1 in every 200 to 500 people in the US has genes that can lead to increased iron accumulation: about 1 per cent of those eventually develop symptoms of the hemochromatosis condition.
Hemochromatosis is an inherited genetic disorder that results in excessive iron absorption and accumulation.
Over time, the build-up of iron in vital organs makes people sick and more susceptible to cancer, diabetes, and liver failure.
Geneticists characterise these people as "homozygous" because they carry two copies of the altered or mutated gene-one from each parent.
People who carry only one copy of the altered gene are surprisingly common, occurring in an estimated 1 in every 10 people in the US, especially those of Northern European origin.
Nutritionist Janet R. Hunt and molecular biologist Huawei Zeng at US government laboratories in North Dakota, part of the Agricultural Research Service, carried out studies to determine whether individuals with only one copy of this genetic mutation could also be at risk of absorbing too much iron.
They tested 359 volunteers by taking DNA samples either from the inside of their cheeks or from blood. Those identified as carriers had their iron absorption measured from regular and iron-fortified meals.
"Carriers of the mutation did not absorb iron differently than volunteers without the mutation, whether or not the meal was iron fortified," report the scientists.
They say this was true for both forms of iron commonly found in foods: "heme" iron, from meat, poultry, or fish; and "non-heme" iron, found in plant foods as well as animal foods.
The researchers claim their findings back US public health policies that allow addition of iron to foods "to help those at the other end of the scale".
There is currently no consensus regarding the extent to which food should be fortified, and the prevailing attitude towards it varies in countries of the industrialised world.
Europe has restrictive legislation regarding the addition of micronutrients to foods. The European Commission proposed a community-wide regulation on addition of vitamins and minerals to foodstuffs in November last year, but due to diverse opinions the proposal never reached its first parliamentary vote. Until this regulation is brought in, European states can ban fortified foods if they show a risk to public health.
The US is more flexible than the European market. Iodine intake, for example, has been enhanced by adding iodine to the bread-making process.