Sept. 22, 2000 -- It tasted awful, but according to mothers everywhere, cured everything. It's cod liver oil derived from, obviously, the liver of cod. Its history as an old wives tale is giving way to science, which is now looking into some of the potential benefits of this legendary fish oil.
Now, researchers have found that babies of mothers who took cod liver oil during pregnancy are less likely to develop type 1 diabetes in childhood, according to a Norwegian study. The researchers, whose work is published in the September issue of the journal Diabetologia, say the big question now is how and why it works.
"I think it is a very interesting study," Marc Hellerstein, MD, PhD, tells WebMD. "I think it is something that has to be explored aggressively, but it is pretty much a preliminary result." Hellerstein, a professor of nutrition at the University of California, Berkeley, was not involved in the study.
Type 1 diabetes, sometimes called juvenile diabetes, is a disease in which the insulin-producing cells in the pancreas are attacked and destroyed by the body's own immune system. Because insulin regulates blood sugar, type 1 diabetics must carefully monitor their blood sugar levels and take insulin shots several times daily. Although scientists are unsure of the exact causes and triggers of diabetes, both genetic and environmental factors are believed to be at fault. Some studies have suggested that several of these factors are at work during pregnancy.
Cod liver oil is an excellent source of vitamin D, which affects the immune system in several important ways and may be tied to the development diseases such as type 1 diabetes. In one study, children who took vitamin D supplements during the first year of life had a reduced risk of developing type 1 diabetes, and some animal studies have shown vitamin D has a protective effect as well.
To explore the association between cod liver oil, vitamin D, pregnancy, and type 1 diabetes, the researchers invited the families of children diagnosed with type 1 diabetes to answer a questionnaire, and 85 responded. They also sent the survey to families with children of the same age, selected at random from the general population. All the families lived in Norway.
The researchers found that children whose mothers had taken cod liver oil while pregnant had only one-third the risk of developing type 1 diabetes compared to other children. There was no association between mothers taking a multivitamin containing vitamin D and type 1 diabetes in their children. Additionally, the researchers didn't find a link between infants who got either cod liver oil or vitamin D supplements during the first year of life and the development of type 1 diabetes.
"The strength of the study is that it is a very potent effect; we are talking about a very substantial reduction, which makes it more interesting. So if it's real, it's big," says Hellerstein, who is also a professor of medicine at the University of California in San Francisco.
"On the other hand, I think there are lots of limitations," he says. One of those limitations is that the numbers are so small that even a few people being misclassified or responding incorrectly to a question could skew the results. Another limitation is that they had no way to account for different doses of cod liver oil or to measure the amount of vitamin D in the blood of the mother or child, according to Hellerstein.
Hellerstein says two ways to discover more about the impact of vitamin D and cod liver oil on the risk for type 1 diabetes would be with animal research and with prospective studies in which women are randomly assigned to take cod liver oil or a placebo oil.
"Before you have every woman [take cod liver oil], you want to make sure it is true. What if there is something that causes a rare toxicity in one out of 30,000 cases?" says Hellerstein. "I think you should never base public policy on one ... study, especially one with as many uncertainties as this one."