One of the mysteries of heart attacks is their seasonality. Before the modern sun avoidance era, there were more than 50% more heart attacks in the winter than in the summer.
Is that because of vitamin D? Doctor Leong Ng, working under senior author Professor Donald Jones, both of the Leicester Royal Infirmary in Leicester, United Kingdom, recently studied vitamin D levels in 1,259 consecutive patients having a heart attack.
First, they found that 74% of the heart attack patients had 25(OH)D levels below 20 ng/ml and thirty-six percent of patients had 25(OH)D values under 10 ng/ml.
After an average 550 day follow-up, the researchers wanted to know if vitamin D levels at the baseline heart attack correlated with death (n=141), heart failure hospitalization (n=111) and/or recurrent heart attack (n=147).
They found that very low 25(OH)D levels predicted heart failure and recurrent heart attack but not death. Second, they found that only those patients with 25(OH)D levels less than 7 ng/ml were at an increased risk for adverse events and that levels above 10 ng/ml were as good as levels above 28 ng/ml in predicted adverse events, about a 40% risk reduction. That is, surprisingly, they showed no benefit of having levels of 20 ng/ml compared to having levels of only 10 ng/ml.
I can’t explain this unusual finding as other studies of the same populations have found significant benefits as quartiles of 25(OH)D levels increase. For example, another study from NHANES showed a graded response with the highest 25(OH)D quartile having significant benefits over the lower quartiles.
Zhao G, Ford ES, Li C, Croft JB. Serum 25-hydroxyvitamin D levels and all-cause and cardiovascular disease mortality among US adults with hypertension: the NHANES linked mortality study. J Hypertens. 2012 Feb;30(2):284-9.
Another study from Harvard showed the same thing in patient with levels above 40 ng/ml having the least risk.
Ginde AA, Scragg R, Schwartz RS, Camargo CA Jr. Prospective study of serum 25-hydroxyvitamin D level, cardiovascular disease mortality, and all-cause mortality in older U.S. adults. J Am Geriatr Soc. 2009 Sep;57(9):1595-603.
A mortality study from Baltimore was even starker. The higher the quartile of vitamin D you were in, the more likely you were to survive every 6 months, all the way to the end of the study’s length of 72 months. In other words the highest quartile was much better than quartile 3 which was much than quartile 2, etc.
Semba RD, Houston DK, Ferrucci L, Cappola AR, Sun K, Guralnik JM, Fried LP. Low serum 25-hydroxyvitamin D concentrations are associated with greater all-cause mortality in older community-dwelling women. Nutr Res. 2009 Aug;29(8):525-30.
So, I don’t think levels above 10 ng/ml are all one needs for cardiovascular benefit. I suspect natural 25(OH)D levels confer the most cardiac protection.