Iodine concentration in tap water, mineral water, and coffee

Sufficient iodine intake is important for thyroid function and, particularly, among women of reproductive age. Water is a universal component of the diet and could be an important source of iodine. Iodine concentration in drinking water varies geographically. It is therefore of nutritional interest to explore the variation and the contribution of iodine from water and beverages.

To analyze the iodine concentrations in tap water, mineral waters, and coffee from different regions of Norway.

Samples of tap water were obtained from different regions of Norway. Six brands of mineral water and several samples of coffee brews were sampled. The iodine concentration was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).

Iodine concentration in tap water varied from below Limit of Quantification to 0.8 μg/100 mL. Five out of six brands of mineral water had low concentrations of iodine, and one brand had a concentration of 38 μg/100 mL. Iodine concentrations in black coffee brews were similar to the tap water. Adding milk or plant-based milk alternatives increased the iodine concentration.

Overall, iodine concentrations in tap water were generally low; however, variations were observed both for inland and coastal regions. A trend was seen for higher iodine concentrations in coastal region compared with inland region. For the average habitual iodine intake in Norway, tap water may not contribute significantly. One brand of mineral water could have considerable impact on iodine intake. Coffee does not contribute substantially more to iodine intake than tap water, unless the brew is added with milk or plant-based milk alternatives that contain iodine.

This study adds new information about iodine dietary sources in Norway. While tap water and black coffee have limited impact due to generally low concentrations, one mineral water brand may contribute significantly to iodine intake.