Cod Liver Oil, the Ratio of Vitamins A and D, Frequent Respiratory Tract Infections, and Vitamin D Deficiency in Young Children in the United States

Abstract

We would like to take this opportunity to respond to the Commentary by Cannell and his distinguished colleagues' (herein referred to as the Commentary). We agree that extensive basic research and adult clinical research performed in the past few decades have demonstrated that the levels of vitamin D required for optimal health are much higher than those needed to prevent rickets in children or osteomalacia in adults; it is also clear that vitamin D deficiency and insufficiency, newly defined for optimal health, are widespread.2 However, as discussed below, we take a different view on several issues criticized by Cannell et al' in their Commentary. COD LIVER OIL Cod liver oil, available without a prescription for hundreds of years, is a valuable source of vitamins A and D, as well as long-chain omega-3 fatty acids,^ all of which may be important in the prevention of respiratory tract illnesses in children (see below. Frequent Respiratory Tract Infections in Young Children). In many populations around the world, cod liver oil continues to be a valuable source of these important nutrients. The across-the-board dismissal of cod liver oil as a supplement advocated by the Commentary ignores this reality. Since the advent of synthetic vitamins in the 1950s, cod liver oil has gone out of favor in the United States, and a valuable source of omega-3 fatty acids has thereby been lost. Only 2% (2 of 94) of children entering Linday's randomized sites supplementation study had a history of cod liver oil use on study entry.'* One teaspoon of cod liver oil historically contained 400 International Units (IU) of vitamin D, and it was used for the prevention and treatment of rickets .^ However, manufacturing processes for the production and purification of cod liver oil have changed substantially over the years.^ Historically, cod liver oil was coldpressed,'^ meaning that the oil was obtained by pressure alone .^ Modern manufacturing methods remove both impurities and vitamins (particularly vitamin D); vitamins A and D may or may not be added back to various degrees. Cod liver oil is not currently regulated or standardized in the United States, and the concentration of both vitamins D and A can vary with the manufacturer, as well as over time. Indeed, as noted in the Commentary,' some modern cod liver oils contain very little vitamin D. One such formulation is Nordic Naturals' Arctic Cod Liver Oil, which contains only 1 to 20 IU of vitamin D per teaspoon.^ On the other hand, the same company's Arctic-D Cod Liver Oil currently contains 1,000 IU of vitamin D per teaspoon,^ whereas in 2005 the formulation bearing the same name contained only 400 IU of vitamin D per teaspoon. In their previous work, Linday et aF-'O-' 1 used Carlson Laboratories' lemon-flavored cod liver oil. Whereas the concentration of vitamin D in this product has remained constant over time at 400 IU per teaspoon, the concentration of vitamin A has steadily decreased. The cod liver oil formulation used in their first supplementation study contained 2,000 to 2,500 IU of vitamin A per teaspoon'; that used in their subsequent research contained only 1,000 to 1,250 IU of vitamin A per teaspoon*; and the current product contains only 700 to 1,200 IU of vitamin A per teaspoon.'2 For children, a formulation that contains 400 IU of vitamin D per teaspoon is consistent with the current recommendations of the American Academy of Pediatrics (AAP).^ Use of higher doses of vitamin D should