Applied Nutrition Sea Moss & Vitamin B12

Sea moss (Irish moss)· evidence: Insufficient

Sea moss (Chondrus crispus, Irish moss) is a red seaweed that is popular on social media. It contains small amounts of minerals, fibre (carrageenan) and iodine, though the amounts vary widely between harvests.

There are almost no human studies of sea moss supplements. Claims about it containing "92 of the 102 minerals" and boosting immunity, thyroid or gut health are not supported by good evidence.

The main real concern is iodine: seaweed can contain a lot, and too much iodine can upset thyroid function.

Typical dose: No established dose. Products usually give 500 to 3,000 mg of dried sea moss.

Safety: Iodine content can vary and high intakes can affect the thyroid. Avoid if you have a thyroid condition or take thyroid medicine, or are pregnant or breastfeeding, unless your GP agrees. Seaweeds can contain heavy metals such as arsenic, so choose brands that test for them.

Research we looked at:
Food Standards Agency. Seaweed and iodine: advice on high-iodine seaweed products.
British Dietetic Association. Iodine: food fact sheet. bda.uk.com
EFSA NDA Panel. Scientific opinion on dietary reference values for iodine. EFSA Journal 2014;12(5):3660.

Vitamin B12· evidence: Strong

Vitamin B12 is needed to make red blood cells and keep the nervous system working. It is found almost only in animal foods (meat, fish, eggs, dairy) and fortified foods, so vegans need a reliable source from fortified foods or a supplement. Older adults and people taking metformin or acid-reducing medicines absorb less B12 from food.

For these groups, B12 supplements are well proven to raise B12 levels and prevent deficiency. If you already eat animal foods and absorb B12 normally, extra B12 has not been shown to boost energy.

The body absorbs only a small share of a large oral dose, which is why many products use 500 to 1,000 µg. Methylcobalamin, cyanocobalamin and other forms all work; there is no good evidence that one form is better for most people. Pernicious anaemia and other absorption problems need a diagnosis and usually injections from your GP.

Typical dose: Adults need about 1.5 µg a day (NRV on labels: 2.5 µg). Vegans: at least 10 µg a day or 2,000 µg a week (Vegan Society guidance). Supplements commonly give 10 to 1,000 µg.

Safety: No upper limit has been set because B12 has very low toxicity; the UK Expert Group on Vitamins and Minerals considered 2,000 µg a day from supplements unlikely to cause harm. Do not self-treat numbness, tingling, a sore tongue or unexplained tiredness: see your GP, as these can be signs of deficiency or pernicious anaemia that needs proper testing. Tell your doctor you take B12 before blood tests, as it raises your B12 result.

Research we looked at:
NHS. Vitamins and minerals: B vitamins and folic acid. nhs.uk/conditions/vitamins-and-minerals/vitamin-b
EFSA NDA Panel. Scientific opinion on dietary reference values for cobalamin (vitamin B12). EFSA Journal 2015;13(7):4150.
Expert Group on Vitamins and Minerals (2003). Safe Upper Levels for Vitamins and Minerals. Food Standards Agency.
NICE guideline NG239 (2024). Vitamin B12 deficiency in over 16s: diagnosis and management.

Iodine· evidence: Moderate

Iodine is needed to make thyroid hormones. Adults need about 140 µg a day in the UK, mainly from milk, dairy, eggs and white fish. Salt in the UK is rarely iodised, so people who avoid dairy and fish, including many vegans, can fall short. Getting enough matters most before and during pregnancy and breastfeeding.

A modest supplement (around 100 to 150 µg) is a sensible way to cover intake for people with low-iodine diets. There is no benefit to taking large amounts, and both too little and too much can upset thyroid function.

Seaweed and kelp products vary widely in iodine content, and some give far more than is needed.

Typical dose: Adults need about 140 µg a day from all sources (NRV on labels: 150 µg). Supplements usually give 75 to 150 µg.

Safety: The NHS advises that 0.5 mg (500 µg) a day or less from supplements is unlikely to cause harm; EFSA's adult upper level from all sources is 600 µg a day. Higher intakes can disturb thyroid function. Anyone with a thyroid condition, or taking thyroid medicine, should speak to their GP before taking iodine.

Research we looked at:
NHS. Others: vitamins and minerals (iodine). nhs.uk/conditions/vitamins-and-minerals/others
British Dietetic Association. Iodine: food fact sheet. bda.uk.com
EFSA NDA Panel. Scientific opinion on dietary reference values for iodine. EFSA Journal 2014;12(5):3660.

Cost per daily dose lets you compare packs of different sizes fairly.Worked out from our current prices.