Q. Should my child be taking fish oil supplements? Which are the best for kids?

A. Fish contain omega-3 fatty acids crucial to brain and vision development. Unfortunately, many fish are contaminated by the toxic metal mercury—which can result in developmental delays and learning disabilities in children—so the U.S. Environmental Protection Agency recommends kids eat no more than two servings per week. Fish with the highest amounts of mercury, such as swordfish, king mackerel, and tilefish, should be avoided altogether. By contrast, many fish oil supplements have been independently tested to ensure purity, so they can be a great way to get omega-3s without risking exposure to toxins.

Any child can benefit from fish oil supplements, which support cognitive development and immune function and lower the risk of diabetes. In addition, fish oil supplements have been shown in studies to help children with asthma, eczema, allergies, attention deficit hyperactivity disorder, behavioral and learning difficulties, and inflammatory bowel disease.

Perhaps the best supplements for kids are the liquid fish oil products, available in fruit flavors that taste surprisingly unfishy. Give these to your child by the spoonful, or if using a plain-flavored oil, pour over steamed vegetables (follow the label for age-appropriate dose). The liquid oil can also be added to a smoothie. However, avoid heating or using fish oil in hot foods, because doing so will destroy the omega-3 essential fatty acids. Older children may prefer to swallow capsules.

Cod liver oil, which contains vitamins A and D in addition to omega-3s, may be the best choice for children who get little sun (the skin makes vitamin D during exposure to sunlight). And even if a child is still breast-feeding exclusively, mom can take fish oil supplements herself to increase the omega-3 fatty acids conveyed through breast milk. If your child has a fish allergy, boost omega-3 fatty-acid intake with walnuts, flax oil, borage oil, and omega-3-enriched eggs.

This Q&A was written by Victoria Dolby Toews, MPH, author of the The Soy Sensation (McGraw-Hill, 2002) and The Green Tea Book (Avery, 1998).