I recently encountered a discrepancy in the American Diabetes Association’s (ADA’s) recommendations regarding conventional versus SI units for HDL cholesterol (1). The article states “raise HDL cholesterol to >40 mg/dl (1.15 mmol/l).” Simple calculation shows that 40 mg/dl = 40 × 0.02586 mmol/l = 1.03 mmol/l, rather than 1.15 mmol/l. The same error is also noted in the 2005 version.
Furthermore, in regard to the ADA’s recommendation to use statin therapy for diabetic patients without overt cardiovascular disease (CVD), the recommendation to treat “regardless of baseline LDL” might have extended beyond the evidence quoted. I find the recommendation’s evidence rather weak, despite a similar recommendation elsewhere (2). For evidence on diabetic patients without overt cardiovascular problems, two studies are listed (3,4). Here is an abbreviated synopsis:
The Heart Protection Study (3) showed cardiovascular benefit of statin therapy for LDL >3.0 mmol/l similar to <3.0 mmol/l. Only 49% of the study’s diabetic subjects were free of overt CVD, and 19% had prior myocardial infarction.
The CARDS (Collaborative Atorvastatin Diabetes Study) (4) showed cardiovascular benefit of statin therapy for LDL >3.1 mmol/l or <3.1 mmol/l. Subjects were without CVD but had at least one of hypertension, retinopathy, proteinuria, or smoking.
I believe the more appropriate interpretation of these two studies is that cardiovascular benefits of the statin therapy on diabetic patients have been shown for LDL < or >3.1 mmol/l (or 3.0 mmol/l, depending on the study). However, the precise lower limit of LDL, where the cardiovascular benefits may or may not persist, has not been explored. Using a threshold of 3.0 mmol/l for LDL is not a replacement for using successively lower thresholds. Using an allegory may help. For example, one cannot claim that since antihypertensive therapy reduces cardiovascular events for patients with blood pressure of >160/100 mmHg, as well as <160/100 mmHg, antihypertensive medications should be used regardless of any baseline blood pressure. Our current ignorance of the lowest LDL threshold of statin’s benefits should not be replaced by the statement that no lower limit to the benefit of LDL lowering exists. A recent study (5) not referenced in the position statement showed cardiovascular benefit of lowering LDL from 3.3 to 2.15 mmol/l, but again, it does not provide an answer as to whether unlimited lowering of LDL may cease to be useful (6).
Hence, I would recommend amending the statement, “For those over the age of 40 years, statin therapy to achieve an LDL reduction of 30–40%, regardless of baseline LDL levels, is recommended (A).” This can be replaced by “For those over the age of 40 years, without overt CVD or cardiovascular risk factors other than diabetes, statin therapy to lower LDL from >3.0 mmol/l to <3.0 mmol/l is advisable. The lowest baseline LDL where statin therapy might cease to be of benefit is currently unexplored and therefore unknown.”
