Dr. Armin Zittermann and colleagues at the Clinic for Thoracic and Cardiovascular Surgery at the Ruhr University Bochum in Germany just studied 4418 consecutive patients who underwent cardiac surgery.
The main complications of cardiac surgery are low output syndrome, heart attack, stroke and death. Eleven percent of the 4400 patients had such complications. Dr. Zittermann measured vitamin D levels on all patients before surgery. He found a U shaped curve in that the patients with 25(OH)D levels between 30 and 40 ng/ml had the best outcomes and the fewest complications. Patients with levels below 20 ng/ml and above 40 ng/ml had the worst outcomes. However, the authors warn that the number of patients with levels above 40 ng/ml was very small.
He found that 38% of the 4400 patients had levels below 12 ng/ml, 32% had levels >12 and <20 ng/ml, but only 3% had levels above 40 ng/ml. Why would patients with levels above 40 ng/ml have bad outcomes? Why did the authors find a U shaped curve?
The authors discussed three possible reasons:
- Enhanced calcium absorption in those with higher levels may worsen prognosis after cardiac surgery. However, none of the patients had hypercalcemia or any difference in calcium levels.
- Higher circulating 25(OH)D may be associated with low free D levels. However, as a general rule, the opposite is true, the higher your 25(OH)D the higher your free D levels.
- Higher 25(OH)D levels have been associated with a genetic variant (APOE 4) that may worsen prognosis. However, that association has never been demonstrated.
I believe a simpler explanation exists. Those with the highest vitamin D levels took cod liver oil and thus had vitamin A toxicity. Cod liver oil intake has a U shaped curve with adult asthma.
Laerum BN, Wentzel-Larsen T, Gulsvik A, Omenaas E, Gíslason T, Janson C, Svanes C. Relationship of fish and cod oil intake with adult asthma. Clin Exp Allergy. 2007 Nov;37(11):1616-23. Epub 2007 Sep 17.
Cod liver oil has also been associated with low bone mineral density.
Forsmo S, Fjeldbo SK, Langhammer A. Childhood cod liver oil consumption and bone mineral density in a population-based cohort of peri- and postmenopausal women: the Nord-Trondelag Health Study. Am J Epidemiol. 2008 Feb 15;167(4):406-11. Epub 2007 Nov 21.
Finally, 51% of Americans have vitamin A excess and 29% have vitamin A toxicity as measured by retinyl esters. Vitamin A excess prevented a favorable relationship between vitamin D and lung cancer mortality.
I have written about the dangers of excess vitamin A in the past:
- Vitamin D, vitamin A, and lung cancer in the USA. Posted on August 31, 2012 by John Cannell, MD
- Newsletter: Vitamin D, vitamin A, and cancer. Posted on January 30, 2010 by John Cannell, MD
- Newsletter: Vitamin A toxicity. Posted on December 15, 2008 by John Cannell, MD
In fact, 16 experts, including Professor Walter Willett, the famous nutrition expert at Harvard, warned about the dangers of cod liver oil in 2008.
Cannell JJ, Vieth R, Willett W, Zasloff M, Hathcock JN, White JH, Tanumihardjo SA, Larson-Meyer DE, Bischoff-Ferrari HA, Lamberg-Allardt CJ, Lappe JM, Norman AW, Zittermann A, Whiting SJ, Grant WB, Hollis BW, Giovannucci E. Cod liver oil, vitamin A toxicity, frequent respiratory infections, and the vitamin D deficiency epidemic. Ann Otol Rhinol Laryngol. 2008 Nov;117(11):864-70. Review.