Seaweed

Studies in people

• Concern

  Thyroid health³

  Eating brown seaweeds like kelp can affect your thyroid, and labels may not warn you.

• Benefit

  Weight and cholesterol⁴

  In adults with overweight or obesity, taking brown seaweed for at least 8 weeks lowered BMI, body fat and cholesterol.

Study type not stated

• Benefit

  Breast cancer risk⁶

  Scientists suggest Laminaria seaweed may help explain lower breast cancer rates in Japan, but have not proven it.

• Open question

  Health benefits need human trials⁷

  Red seaweed colours may work in food, but scientists still need human studies to confirm any health benefit.

• Benefit

  Nutrients and immune benefits⁸

  Seaweed is packed with minerals, vitamins and fibre, and compounds in it may fight germs and swelling.

Found in some samples or products

These come from where it was grown, how it was processed or cooked, or what it was made into. They are not about the ingredient itself, so the signal does not count them.

• Washing reduces contamination⁹

  Seaweed can carry microplastics, and washing it in water may help remove some.

Single cases of misuse or overdose

One person or one incident, such as an accidental overdose or a mistake in a kitchen or factory. They are real, but a single case does not show what happens at normal amounts, so the signal does not count them.

• Skin colour change⁵

  A woman who ate lots of carotene-rich seaweed turned orange-yellow, and her skin returned to normal after she stopped.

How it’s made and used

• How much iodine the body absorbs¹⁰

  In animal studies, how much iodine from seaweed the body absorbs varied a lot between different seaweeds.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.