Mineral nutrient content and iron bioavailability in common and Hawaiian seaweeds assessed by an in vitro digestion/Caco-2 cell model

•Mineral content and iron (Fe) bioavailability was assessed in seaweeds and spinach.•Ten of 13 seaweeds analyzed contained more Fe than spinach per gram of dry matter.•Efficiency of iron absorption was low in seaweeds, similar to that in spinach.•Only nori and sea lettuce provided greater amounts of bioavailable Fe than spinach.•Arsenic levels were high in several seaweeds limiting their use as a source of Fe.

Iron (Fe) deficiency remains a public health problem. Deficiency is often due to low iron intake and/or iron bioavailability. Seaweeds are known to be rich in iron, but its bioavailability is poorly understood. Our objective was to evaluate common, edible seaweeds from Asia, Hawaii, and Maine as sources of iron by comparing iron content and bioavailability to spinach. Ten of 13 seaweeds analyzed contained more iron than spinach. Iron content ranged from 73 to 3490 μg/g dry matter (DM). Twenty percent of the Daily Value for iron could be obtained from just 4.3 g of dry sea lettuce, 5.1 g of dry rockweed, 9 g of dry wakame, or 13 g of dry nori. However, in vitro bioavailability studies indicated that, due to low absorption efficiencies, not all seaweeds would provide greater amounts of bioavailable Fe than spinach. Notable exceptions were nori and sea lettuce which provided 3 and 5-fold more bioavailable Fe, respectively. In addition, bioavailability was significantly enhanced by vitamin C in these two seaweeds. We conclude that certain seaweeds could be good sources of bioavailable iron. However, many seaweeds contained high levels of arsenic or other minerals which could limit regular consumption as a safe source of iron.