Monday, 26 August 2013

False dichotomies: serum cholesterol level vs all-cause mortality. Cause or effect?

Here are some plots from the MRFIT study.
From http://sph.bu.edu/otlt/MPH-Modules/PH/PH709_Heart/PH709_Heart5.html

Although the relative risk (RR) for coronary heart disease (CHD) and cardiovascular disease (CVD) mortalities increase with serum total cholesterol (TC) level, all-cause mortality follows a U-curve.

According to Low Serum Cholesterol and Mortality: Which Is the Cause and Which Is the Effect?, certain illnesses that increase mortality lower TC levels. This is the Iribarren hypothesis.

According to Cholesterol and all-cause mortality in elderly people from the Honolulu Heart Program: a cohort study, TC that's low and is still low 20 years later results in a 64% increase in the RR for mortality relative to TC that's intermediate and is still intermediate 20 years later.

Table 4 Relative risk for mortality based on change in cholesterol between examinations three and four
Is low TC level the cause of, or the effect of fatal illnesses? I think that it's both. Cholesterol is an important substance, as a severe lack of it is bad news, as per Smith–Lemli–Opitz syndrome. If certain illnesses result in a depletion of cholesterol and cholesterol synthesis is too low, there's insufficient cholesterol to allow recovery.

Interestingly, TC that's low but is intermediate 20 years later results in a 30% increase in the RR for mortality, whereas TC that's low but is high 20 years later results in a 5% increase in the RR for mortality.

P.S. There's a false dichotomy for vitamin D level vs illness. Ditto for carbohydrates vs calories.

4 comments:

ProudDaddy said...

Given that statins don't help us over 70 folks without heart disease, what would the MRFIT curves look like for men over 70?

Nigel Kinbrum said...

I can't quantify it, but the left end of the all-cause mortality curve rises with increasing age, which shifts the minimum to the right.



There are some more studies (including Schatz et al) on TC vs mortality in http://nigeepoo.blogspot.co.uk/2011/02/mums-proposed-ketogenic-diet-for.html

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