The following information has been prepared by Jamieson Laboratories to answer your questions about recent reports on the study “Cod Liver Oil, Vitamin A Toxicity, Frequent Respiratory Infections, and the Vitamin D Deficiency Epidemic.”
What was the purpose of the study?
The study “Cod Liver Oil, Vitamin A Toxicity, Frequent Respiratory Infections, and the Vitamin D Deficiency Epidemic” was designed to examine previous epidemiological data suggesting Vitamin D may reduce the incidence of colds and respiratory infections. Among their observations, the authors propose that pharmacologic doses of Vitamin D might effectively treat influenza. Their conclusion is that current maintenance-dose recommendations of 1,000 IU prevent Vitamin D deficiency.
In what context did the issue of Vitamin A and Cod Liver Oil enter the researchers’ analysis?
In the course of examining scholarship on Vitamin D and its effect on colds and flu, the scientists reviewed a 2004 study by Lindsay et al. that investigated the impact of cod liver oil, plus a daily multivitamin-mineral with selenium, on the incidence of upper-respiratory pediatric visits among young inner-city Latino children.
The authors' interest in the 2004 study is, in part, because Lindsay showed that the combination of 600 to 700 IU of Vitamin D, along with a maximum of 3,500 IU of Vitamin A (given as cod liver oil and a multivitamin), reduced the incidence of upper respiratory infections. The benefit, however, was less than it was among participants taking higher doses of Vitamin D alone.
Why did the authors care about the impact of Vitamin A?
It appears that the authors’ main concern was to put the Lindsay study in a context that did not undermine their own hypothesis about Vitamin D. To that end, they suggested that the Vitamin A found in Cod Liver Oil acted against the Vitamin D, thereby reducing its effectiveness. This is an issue raised by other studies.
Why has this analysis raised alarm about Vitamin A?
In taking their argument about Vitamin A to its logical extreme, the researchers introduced data suggesting that Vitamin A at high doses had previously been associated with bone ailments and other illnesses. In conclusion however, the authors noted that only “absurd” amounts of Vitamin A, through combined sources, have been known to cause problems.
When combined with Vitamin D, Vitamin A caused no known adverse health effects. This may explain why a teaspoon of Cod Liver Oil, which has naturally occurring Vitamin D, does not pose any health risk, even though it typically contains Vitamin A ranging from 1,200 µg (4,000 IU) to 3,000 µg (10,000 IU) and up to 9,000 µg (30,000 IU).
Media reporting has also inflamed this story. There have been alarming headlines that do not correspond to the research itself, but which have led many people to unwarranted concern about the use of Cod Liver Oil supplements.
In fact, the study’s main purpose is to draw attention to the need for increased Vitamin D supplementation. The authors advise that manufacturers of supplements and fortified foods balance doses of Vitamins A and D. What is sorely missing from their recommendation, however, is clinical data supporting specific doses for these two nutrients.
What are the current recommended adult intakes of Vitamin A?
Currently, Health Canada recommends a maximum daily intake of 3,000 µg (or 10,000 IU) of Vitamin A — the equivalent of a teaspoon of Cod Liver Oil. According to Health Canada, Vitamin A is a factor in good health and is important in the development and maintenance of teeth, skin and bones, and it supports immune function. Vitamin A also maintains eyesight and night vision.
The Council for Responsible Nutrition’s 1999 publication Vitamin and Mineral Safety (Second Edition) supports these claims, noting that Vitamin A plays two distinct roles in eye health and function, first as a retinol-opsin complex that serves as a phototransducer, and also in the health and function of the various eye membranes. “In the first case, deficiency of Vitamin A in the retina leads to night blindness,” the authors write. “In the second, deficiency can lead to xerophthalmia, with loss of the basic integrity of the eye structure and possible total blindness.” In fact Vitamin A deficiency is the foremost cause of preventable blindness in the world.”
What are the Vitamin A potencies used in Jamieson products?
All Jamieson Vitamin A products are made according to potency levels approved by Health Canada as safe and effective. No product exceeds 3,000 µg (10,000 IU) of Vitamin A. Our multivitamin-mineral formulations contain no more than 1,000 µg (or 3,000 IU) of Vitamin A. Of Jamieson’s four Vitamin A products, three are already formulated with Vitamin D.
What are the current recommended adult levels of Vitamin D?
According to Health Canada, Vitamin D is a factor in the maintenance of good health and specifically aids in the development and maintenance of bones and teeth by helping the body absorb and use of calcium and phosphorus. Calcium intake when combined with sufficient Vitamin D, a healthy diet and regular exercise may reduce the risk of developing osteoporosis.
With studies emerging on the benefits of Vitamin D, health organizations recommend a daily dose of 1,000 IU of Vitamin D for people who live in Canada. Health Canada recently raised the accepted potency of Vitamin D supplements from 400 IU to 1,000 IU to match these findings.
Consumers can experience better health through the responsible use of supplements. Jamieson Laboratories is Canada’s leading manufacturer of advanced health products. Our premium formulations are manufactured in Windsor, Ontario, according to a minimum of 360 quality-assurance tests that guarantee each product’s safety, full potency and absolute clinical purity.
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