Itt írjon a(z) iodine_deficiency_fetus-ról/ről

Effect of iodine deficiency on fetal development during pregnancy

Iodine is an essential part of life. This micronutrient is required for the biosynthesis of thyroid hormones and contributes to normal growth and development. The body itself cannot produce iodine, and we are therefore at risk of experiencing deficiency if our diet doesn't reach the requirements. Pregnant and lactating women are particularly vulnerable, due to increased iodine demand. (Toloza et al, 2020)

According to research, it is estimated that two billion suffer from iodine deficiency. (Andersson et al, 2005) The most visible symptom of the insufficiency is the goiter, an increased size of the thyroid gland. Still, the most common problem is the impaired neurodevelopment, especially in early life. (Zimmerman, 2011)

When a female is carrying a child the demand for iodine will significantly increase. The reason for this is the amplified production of maternal thyroid and the loss of iodine in the urine. The fetus itself also requires iodine which is another reason why pregnant women must consume more iodine. A maternal iodine deficiency can be classified depending on the severity. It can range from mild defects in motor development, to severe cases resulting in cretinism. (Lee and Pearce, 2015)

The recommended amount for iodine intake during the different life stages can be seen in Table1:

Table 1: Visual representation of recommended amount of Iodine (Lyons, 2021)

Thyroid synthesis

The medical explanation for iodine importance is its effect on the thyroid hormone synthesis. In the thyroid gland there are produced two important hormones, the triiodothyronine (T3) and the thyroxine(T4). They act on almost all cells in the body, affecting protein synthesis, metabolism, and bone growth. Both hormones are partly composed of iodine, and a decrease in the mineral would therefore have a negative impact on the T3 and T4 production. (Toloza et al, 2020)

An active pump mechanism transports iodine into the thyroid. This pump also works as a trap, to capture iodine ions in the thyroid gland. Under normal circumstances this means that there will be 40 times higher iodine concentration in the thyroid gland compared to the blood. But when the body is iodine deficient this gradient increases to 200 times more iodine! Lysosomal peroxidase converts iodine ion to atomic ion. The atomic ion then binds to the tyrosine residues of the thyroglobulin and monoiodotyrosine (MIT) is produced. With 2 iodine atoms, diiodotyrosine (DIT) is formed. MIT + DIT = triiodothyronine (T3) and DIT + DIT = tetraiodothyronine (T4). These are then endocytosed into the epithelium where they are degraded intracellularly and T3 and T4 are secreted to the bloodstream. Thyroid stimulating hormone (TSH) stimulates almost every step of the thyroid synthesis and storage.

Thyroid hormones are essential for many processen in the body. Basic metabolic rate can increase up to 60% in the presence of thyroid hormones, mainly because of the increased activity of NA+/ K+ ATPase. Glyconeogenesis and glycogenolysis are increased, the lipid metabolism is increased as a whole and the fatty deposit is reduced. In the protein metabolism the thyroid hormones stimulate both synthesis and breakdown of the proteins.

In case of a pregnant female, there will be deiodinase which will convert T4 to T3 when it goes through the placenta. In the fetus T3 is the one binding to cell receptors and starts the development of different parts of the nervous system. Therefore, a lack of iodine which results in hypothyroidism can result in an undeveloped neural system in the fetus, which will be permanent. (Toloza et al, 2020)

Range of iodine deficiency in pregnancy

The iodine deficiency outcomes can be looked on as an iceberg, see Figure 2. Where the top and visible part is cretinism which occurs in 1-10% in severe iodine-deficiency. Then you have the part which is “not visible” and under water, which is the less severe brain damage. The part under water is much bigger and occurs in 30% of the cases of iodine-deficiency. (Chen and Hetzel, 2010) In other words, the iodine deficiency can be placed on a spectrum. It can range from lesser cognitive defects to different types of iodine deficiency disorders (IDDs´) (Chen and Hetzel, 2010).