The United Kingdom Expert Group on Vitamins and Minerals (EVM) last evaluated vitamins and minerals for safety in 2003 and set a so-called Safe Upper Level (SUL) or Guidance Level for each micronutrient, provided sufficient data were available. This SUL or Guidance Level reflects the safe maximum amount of a micronutrient that will not cause any side effects when taken daily from all sources for a lifetime.
| The maximum safe daily intake for iron is 17 mg. The maximum safe daily intake for iron considers only the intake of iron from dietary supplements and fortified foods in addition to the intake from conventional foods. |
The above safe maximum daily intake applies to divalent iron and explicitly does not apply to individuals who are at increased risk of iron overload (e.g., hemochromatosis/iron storage disease).
The data from the NVS II (National Nutrition Survey II, 2008) on the daily intake of iron supplements make it clear that, in addition to the undersupply of iron in the German population (see under “Supply situation”), part of the population (5 to 10%) also consumes quantities of iron in the form of dietary supplements above the intake recommendations and the safe maximum daily intake.
Iron overload is at least as big a problem in the population as iron deficiency, because the body’s iron status can only be regulated by intake, since there are no effective mechanisms for excreting excess iron.
At the same time, a high iron intake via conventional nutrition is not associated with undesirable side effects, since the absorption rate in the intestine decreases with increasing intake. High iron intake in the form of supplements may be less tightly regulated and lead to higher absorption.
The LOAEL (Lowest Observed Adverse Effect Level) – the lowest dose of a substance at which adverse effects were just observed – is 70 mg of iron per day from all sources. The LOAEL for iron in supplement form is 60 mg per day. A tolerability study with the endpoint of gastrointestinal effects was used as a reference here, i.e., this LOAEL does not take into account long-term consequences of a permanently excessive iron intake such as cardiovascular disease or an increased risk of cancer.
Adverse effects of excessive iron intake have been observed as constipation, nausea, diarrhea, and vomiting. In some studies, skin rash also occurred.
In these cases, the severity of symptoms increases with higher iron intake. Gastrointestinal side effects such as constipation and vomiting occurred at doses between 50 and 220 mg of iron per day, with the frequency of symptoms increasing with larger amounts of iron. The first milder skin reactions occurred after administration of 30 mg of iron, while an amount of 10 mg did not result in any adverse reactions.
In addition to acute ingestion of high amounts of iron, high body iron stores also pose a potential risk. High iron stores are discussed in connection with an increased risk of atherosclerosis (hardening of the arteries), myocardial infarction (heart attack), colorectal carcinoma (malignant tumor in the intestine), Parkinson’s disease, and type II diabetes mellitus.
Scientific confirmation of the potential risk of high iron stores is still pending. In particular, current studies suggest that a relationship between high iron stores and an increased risk of cardiovascular disease is likely.
