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Department of Family Medicine
Tripler Army Medical Center
Honolulu, HI

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.

References

1. Oh R. Vitamin D insufficiency as a cause of hyperparathyroidism. Am Fam Physician 2005; 71: 46,49.[Medline]

2. Oh R. Practical applications of fish oil (omega-3 fatty acids) in primary care. J Am Board Fam Pract 2005; 18: 28–36.[Abstract/Free Full Text]

3. Feskanich D, Singh V, Willett WC, Colditz GA. Vitamin A intake and hip fractures among postmenopausal women. JAMA 2002; 287: 47–54.[Abstract/Free Full Text]

4. Michaelsson K, Lithell H, Vessby B, Melhus H. Serum retinol levels and the risk of fracture. N Engl J Med 2003; 348: 287–94.[Abstract/Free Full Text]

5. Rothman KJ, Moore LL, Singer MR, et al. Teratogenicity of high vitamin A intake. N Engl J Med 1995; 333: 1369–73.[Abstract/Free Full Text]

6. Omacor. Consumer drug information sheet. U.S. Food and Drug Administration. Accessed on July 4, 2005 at: http://www.fda.gov/cder/consumerinfo/druginfo/omacor.htm

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