To the Editor: I thank Ms. Ross for the comments on my article. I too feel strongly that physicians under-appreciate and under-recognize mild vitamin D deficiency.1 Although cod liver oil is rich in vitamin D, most formulations do not have enough omega-3 fatty acids (FA) for it to be practical in clinical use. In an informal survey I performed, I found that typical preparations contain approximately 50 to 90 mg of omega-3 FA (compared with 300 mg in fish oil).2 To reach 1 to 4 g of omega-3 FA (doses needed for secondary prevention of cardiovascular disease, rheumatoid arthritis, and hypertriglyceridemia)2 one would have to ingest 10 to 40 capsules of cod liver oil daily.

In addition, cod liver oil contains approximately 135 IU of vitamin D and 2500 IU of vitamin A in each capsule. Toxic doses of vitamin A can occur if cod liver oil is given in doses typical for treatment of hypertriglyceridemia and rheumatoid arthritis (2 to 4 g). Studies have also linked chronic daily vitamin A intake to increased fracture risk and teratogenicity.3–5 Cod liver oil may potentially be used for conditions requiring supplementation of vitamin A and D but should generally be avoided for conditions requiring high levels of omega-3 FA. Other formulations may contain higher levels of omega-3 FA, but consumers and physicians must be especially cognizant of the amount of vitamin D and vitamin A that are contained in the preparation to avoid toxicity.

Even typical fish oil supplements may be difficult to provide 2 to 3 g of omega-3 FA, and physicians should consider prescribing highly concentrated formulations. Recently, the Food and Drug Administration has approved a prescription form of omega-3 FA containing approximately 900 mg of omega-3 FA in each capsule.6 Although only approved for the treatment of hypertriglyceridemia, physicians can also consider this formulation in off-label uses for secondary prevention of cardiovascular disease and rheumatoid arthritis to minimize the number of capsules that patients have to take.