The idea that cholesterol causes cardiovascular disease comes from studies which find that higher cholesterol levels are linked with raised risk of heart disease and stroke. However, it’s important to bear in mind that such studies are ‘epidemiological’ (also termed ‘observational’) in nature, which means we cannot infer from them that cholesterol causes heart disease (just because two things are associated with each other, that does not necessarily mean one is actually causing the other).
Also, cardiovascular disease is a major killer, but it’s not the whole story. If we want to assess the impact of any factor on health, I think it pays to take as wide a view as possible. We can do this by looking at that factor’s relationship with overall risk of death. This is especially important for cholesterol, as low levels of this substance in the bloodstream are actually associated with heightened risk of potentially fatal conditions including cancer.
These considerations seem to be even more important in the elderly, as previous evidence has linked lower cholesterol levels with enhanced mortality. One such study was published late last year in the journal Clinical Nutrition . In this study, elderly individuals (average age 81) admitted to hospital had their total cholesterol levels assessed. They were then monitored for an average period of about 3½ years.
Cholesterol levels were split into ‘quartiles’ (each quartile represents 25 per cent of cholesterol values, with the ‘top quartile’ representing the top 25 per cent of cholesterol values while the ‘bottom quartile’ represented the lowest 25 per cent of cholesterol values).
The mortality rate in those of in the lowest quartile (total cholesterol of 1.76-4.00 mmol/l) was about 93 per cent, but in the group in the top quartile (total cholesterol of 5.5-8.3 mmol/l) it was significantly lower at 76 per cent.
The authors calculated that each 1 mmol/l increase in cholesterol was associated with a more than 15 per cent reduction in risk of death.
Now, just to be clear, this is epidemiological evidence, again, and it cannot be used to infer that raised cholesterol actually protects against death. One of the reasons for this is that lowered cholesterol can be a sign of malnutrition (not uncommon in the elderly). In this study, low cholesterol was also found to be associated with lower levels of the blood protein albumin (low albumin suggests malnutrition). However, if malnutrition is the explanation, then it does raise at least some questions about the promotion of low-fat (sometimes semi-starvation) diets for cholesterol reduction. Most importantly, these diets have, as whole, not been found to reduce mortality, and there is some evidence that they may in fact be harmful to health.
The authors of this study make mention of the supposedly dangerous low-density lipoprotein (LDL) form of cholesterol. Specifically they allude to the fact that LDL cholesterol comes in different forms, ranging from small, dense forms that are believed to have potential to damage blood vessels, up to much larger, lighter forms that do not. They point out that long-lived individuals have been found to have a preponderance of presumably non-harmful LDL in their bloodstreams.
In the final analysis, we don’t know from this sort of evidence what the truth is. However, this sort of evidence should, I think, be more widely known, and should also cause us to question this vogue for driving cholesterol levels down. Cholesterol is an innate body constituent present in every cell membrane and is a major component in the brain. It is also a constituent of several key hormones, vitamin D and bile (for the digestion of fat). There seems little doubt that low levels of this substance can genuinely compromise health.
The bottom line is that cholesterol reduction is not without risk, though it’s something easy to forget that when we are bombarded with information about the supposedly perilous nature of cholesterol and the need to ‘keep it under control’.
1. Weiss A, et al. Serum total cholesterol: A mortality predictor in elderly hospitalized patients. Clin Nutr 2012 Nov 23 [epub ahead of print]