Pregnant and lactating women should make sure they receive enough iodine

Dipl. oec. troph. Silke Röhl and Prof. Dr. med. Beate A. Schücking, Universität Osnabrück, Germany.

“In the human organism, iodine is mainly a component of the thyroid hormones thyroxine and triiodothyronine, which are essential for energy metabolism and cell growth, and interact with many other hormones, such as insulin. Thanks to its high affinity for oxygen, iodine has an antioxidant effect and can, for example, protect polyunsaturated fatty acids against oxygen radicals (1, 2). Outside of the thyroid gland, iodine mainly protects against microbes in the secretion of exposed mucous membranes

(3, 4). For example, the iodine concentration in saliva is 20 to 100 times higher than in blood plasma. Effective concentrations are also shown in the tear film (5), nasal mucus, saliva, gastric juice (6-8), and the rectal mucosa. Iodine may also have a similar effect in the lungs. A chronically elevated iodine level can lead to a reduction in sperm production and function (9). Its spermicidal effect in the uterine mucosa is cycle-dependent, which explains why the vaginal secretions are the only ones that show no increased iodine levels. The function of iodine in the gonads and in the islet cells of the pancreas is unclear (10, 11). Iodolactam, which is synthesized from arachidonic acid, inhibits the growth of certain cells and accelerates their death, which appears to especially play a role in cancer cells (12). Although elemental iodine has no documented effect on the immune system itself, iodine deficiency leads indirectly to a change in the delayed-type immune response. The underlying mechanism for this is unknown (13, 14).

The physiological uptake of iodine from the diet is very low: it is one of the trace elements with only 10 to 20 mg distributed throughout the entire body (15). To ensure iodine supply, eating fish once or twice a week is recommended. Milk and milk products are also good iodine sources and should therefore be a part of the daily diet. In addition, the use of iodized salt and food products made with iodized salt is recommended. Breathing is the second major source of iodine. There are about 0.5 μg iodine/m3 in the air; this concentra-tion is much higher close to the ocean.

During pregnancy and lactation, a special distribution of iodine occurs via the placenta in the fetus and via breast milk, respectively. We can thus interpret that the iodine affinity in the uterus/placenta and breast milk-producing glands is at its highest during this time. With regard to a requirement-based iodine supply, pregnant and lactating women are considered a risk group (16–18). Since the increased iodine requirements – i.e. 230 μg or 260 μg per day – can only be guaranteed via dietary intakes by a scrupulous selection of foods, daily supplements of iodide are recommended for pregnant and lactating women. An additional intake of 100 to 200 μg iodine per day is usually necessary (19). Studies that address the issue of iodide supple-ments during pregnancy have shown significant supply deficits in pregnant women over many years. In Germany, for example, 42% of the women surveyed took no iodine supplements (20). Over 80% of women surveyed achieved less than 50% of the recommended intake of 230 μg (21). Iodine supplementation among breastfeeding women was, at 49.6%, significantly lower than that of pregnant women (22). The most important factors influencing dietary supplementation were consistent implementation and an doctor’s explicit recommendation. To improve iodine supply, pregnant women and nursing mothers, especially with lower levels of education, should be more intensively advised to take iodine supplements.”

Based on: Röhl S. and Schücking B. A. Jodversorgung bei Schwangeren und Stillenden. Ernährungs Umschau. 2011; 58:596–601.