Friday, August 15, 2008

Cardiovascular Risk Factors on Kitava, Part II: Blood Lipids

The findings in the previous post are all pretty much expected in a population that doesn't get heart disease. However, things started to get interesting when Lindeberg's group measured the Kitavans' serum lipids ("cholesterol"). Kitavan and Swedish total cholesterol is about the same in young men, around 174 mg/dL (4.5 mmol/L). It rises with age in older Swedish men but not Kitavans.

Doctors commonly refer to total cholesterol over 200 mg/dL (5.2 mmol/L) as "high", so Kitavan men are in the clear. On the other hand, Kitavan women should be dying of heart disease left and right with their high middle-age cholesterol of 247 mg/dL (6.4 mmol/L)! That's actually higher than the value for Swedish women of the same age, who are far more prone to heart disease than Kitavans.

The fun doesn't stop there. Total cholesterol isn't a good predictor of heart attack risk, but there are better measures. LDL on Kitava is lower in males than in Sweden, but for females it's about the same until old age.  HDL is slightly lower than Swedes' at middle and old age, and triglycerides are higher on average. Judging by these numbers, Kitavans should have cardiovascular disease (CVD) comparable to Swedes, who suffer from a high rate of cardiovascular mortality.

Kitavan smokers had a lower HDL than nonsmokers, yet still did not develop CVD. Smoking is considered one of the most powerful risk factors for cardiovascular disease in Western populations.  I think it's worth noting, however, that Kitavans tend to be light smokers.

These data are difficult to reconcile with the hypothesis that certain patterns of blood lipids cause CVD. Kitavans, particularly the women, have a blood lipid profile that should have them clutching their chests, yet they remain healthy.

There is a theory of the relationship between blood lipids and CVD that can explain these data. Perhaps blood lipids, rather than causing CVD, simply reflect diet composition and other lifestyle factors. Both on Kitava and in the West, low HDL and elevated triglycerides imply a high carbohydrate intake. Low-carbohydrate diets consistently raise HDL and lower triglycerides. On Kitava, carbohydrate comes mostly from root crops. In the West, it comes mostly from processed grains (typically wheat) and sugar. So the blood lipid pattern that associates best with CVD and the metabolic syndrome in the West is simply a marker of industrial food intake.

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