I know that some doctors and scientists would have us believe that, where cholesterol is concerned, “lower is better”, but I have real difficulty mustering any enthusiasm for this stance. And one major reason for this is the fact that low levels of cholesterol are associated with enhanced risk of death, perhaps most notably from increased risk of cancer [1-4]
Some have suggested that low cholesterol is a marker for “frailty” in the elderly. However, this concept is contradicted by evidence which finds that the association between low cholesterol levels and enhanced risk of mortality occurs in younger people too .
It has also been suggested the relationship between low cholesterol and enhanced risk of mortality is the result of “reverse causality” i.e. that disease processes such as cancer can cause low cholesterol, even up to a decade before the underlying condition is diagnosed (sometimes referred to as “Iribarren’s hypothesis”). However, long-term studies provides evidence which counters this concept .
It should perhaps be borne in mind that cholesterol is a component in cell membranes, and an essential constituent of steroid hormones and vitamin D (which increasing evidence suggests has disease-protective properties, particularly with regard to cancer prevention).
The fact that cholesterol is a component in cell membranes might have significance to many biological processes, including neurological ones. It is possible, in theory at least, that low levels of cholesterol might somehow disturb the function of nerves in the brain. Could low levels of cholesterol, then, lead to mental health issues?
In a study published this month, the relationship between cholesterol levels and depression was assessed in a group of French men and women over the aged 65 or older . The assessment continued for 7 years. This study found that:
1. In men, low levels of low density lipoprotein (LDL) cholesterol (supposedly “unhealthy” cholesterol) were associated with an increased risk of depression
2. In women, low levels of high density lipoprotein (HDL) cholesterol (supposedly “healthy” cholesterol) were associated with an increased risk of depression
Now, epidemiological studies of this nature cannot be used to determine that lower cholesterol studies cause depression. However, bearing in mind cholesterol’s role in brain cell health, the potential for a “causal” link does indeed exist.
This study, by the way, is not the only one to link low cholesterol levels with mental health issues. For example, last year a Spanish review  of the evidence concluded that: “It is shown that low cholesterol levels in serum are associated and related to different neuropsychiatric disorders. Lowered cholesterol levels seem likely to be linked to higher rates of early death, suicide, aggressive and violent behaviour, personality disorders, and possibly depression, dementia and penal confinement among young males.”
Now, some will claim that any problems with lower cholesterol need to be balanced with the “benefits” of this, in terms of reduced risk of heart disease. We do need to be slightly wary of this argument, though, because there is actually quite a lot of evidence that in the elderly, higher cholesterol levels are not necessarily associated with an enhanced risk of cardiovascular disease and/or overall risk of death [9-18].
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3. Yang X, et al. Independent associations between low-density lipoprotein cholesterol and cancer among patients with type 2 diabetes mellitus. Canadian Medical Association Journal 2008;179(5):427-437
4. Schatzkin A, et al. Serum cholesterol and cancer in the NHANES I epidemiologic follow up study. National Health and Nutrition Examination Survey. Lancet 1987;2:298-301
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