Q. I am pregnant and have high cholesterol. Is it OK to take fish oil supplements?

A. Cholesterol levels tend to rise during pregnancy because of pregnancy hormones rather than from foods eaten.

Fish and fish oil supplements don't actually lower cholesterol levels even in those who are not pregnant. Instead, they reduce another type of blood fat implicated in heart disease called triglycerides. They also reduce heart attack risk by thinning blood and reducing inflammation.

Eating fish during pregnancy contributes to the baby's brain development and vision. However, some fish have high levels of mercury and need to be avoided during pregnancy. Mercury can damage the brain in unborn babies and young children, resulting in learning and behavior problems.

Large predatory fish contain the most mercury. These include kajiki (Pacific blue marlin), shark and swordfish (shutome). The state Department of Health recommends pregnant or breastfeeding women, those planning to become pregnant, and children younger than 5 avoid these fish.

A portion of fish is 6 ounces for adults and 3 ounces for children. 'Ahi, ono and opah should be eaten only once in two weeks. Aku, mahimahi, canned tuna, butterfish and striped marlin are examples of fish that can be eaten once per week. Salmon, sardines, moi and fish small enough to fit in a frying pan whole are examples of fish that contain little or no mercury and can be eaten anytime.

Although some fish contain mercury, this does not appear to be true of fish oil supplements. Consumer Labs, an independent laboratory, tested 42 brands of fish oil capsules and found that all were free of mercury and PCB contamination. One brand failed the test because of spoilage and another because it contained less omega-3 (the active ingredient) than stated on the package. To see which brands passed, go to www.consumerlabs.com.

Pregnant women should talk with their obstetricians before taking any supplements. Excess omega-3 fatty acids could thin the blood, resulting in potential bleeding during pregnancy. The best way to get your omega-3 fatty acids may be to consume 6 to 12 ounces of low-mercury fish each week.

Note: In my May 31 prescriptions column, I wrote that the form of niacin needed to lower cholesterol (nicotinic acid) was only available by prescription. A reader has informed me that a product called Slo-Niacin is sold over the counter and contains nicotinic acid in similar doses to prescription products. If you use this product, be sure to tell your physician so that liver function tests can be performed periodically.

Amy Tousman is a registered dietitian and certified diabetes educator with Nutrition Unlimited in Kailua. Hawai'i experts in traditional medicine, naturopathic medicine and diet take turns writing the Prescriptions column. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.