A couple of weeks back one of my blog posts highlighted a study from England in the UK which found that total cholesterol levels had no relationship with risk of death from heart disease. Moreover, higher cholesterol levels were associated with a reduced risk of stroke. Such findings obviously ask serious questions about the concept that cholesterol causes things like heart attacks and strokes. It also casts considerable doubt on the idea that we should be attempting to drive our cholesterol down.
Currently in the UK, as in some other countries, we are advised to ensure our total cholesterol levels are less than 5.0 mmol/l (193 mg/dl). I’ve lost count of the number of fit, healthy individuals with no hint of illness who have told me they have a ‘raised’ cholesterol. Average cholesterol levels in adults in the UK are about 6.0 mmol/l. This means that significantly more than half adults have ‘raised’ cholesterol.
Remember, cholesterol is an essential body constituent: it is a component in the membranes of all cells, and a constituent of key hormones (e.g. testosterone, oestrogen and cortisol) and vitamin D. It is also an important component of the brain and nervous system. Does it seem right that an essential body constituent present a normal levels in the body somehow poses dire risks to health?
Well, not according to the study I wrote about a couple of week’s back, and not according to another study I am going to highlight here.
This particular study was conducted in Norway. It assessed more than 52,000 Norwegians over a 10-year period . Part of the study was to assess the relationship between total cholesterol levels and risk of death from cardiovascular disease (mainly heart attacks and strokes) and death from heart disease alone. Norway also uses 5.0 as their cholesterol cut-off. Risk of death in different cholesterol bands was assessed, the lowest band being levels of less than 5.0 mmol/l, while the highest band was levels of 7.0 mmol or more.
In both men and women, there was simply no relationship between cholesterol levels and risk of death from these things. Individuals with cholesterol levels of 7.0 mmol/or more were no more likely to die from cardiovascular disease than those with cholesterol levels less than 5.0 mmol/l.
These results are interesting, but the researchers went further by assessing the relationship between cholesterol levels and overall risk of death (overall mortality). This is important here because low cholesterol levels are actually associated with an increased risk of certain conditions including cancer and a type of stroke known as ‘haemorrhagic stroke’.
In the Norwegian study, overall risk of death was not any higher in men with cholesterol levels of 7.0 mmol/l or higher than in individuals with levels of less than 5.0 mmol/. Actually, the lowest risk of death in men was seen in individuals with cholesterol levels in the 5.0 – 5.9 mmol/l. In this group, overall risk of death was actually 23 per cent lower than in men with the lowest cholesterol levels.
In women, the results were somewhat different: the higher the cholesterol level was, the lower the overall risk of death. However, this finding only became statistically significant in the category of cholesterol levels of 7.0 mmol or higher. Compared to women with cholesterol levels less than 5.0 mmol/l, the women with the highest cholesterol levels were 28 per cent less likely to die overall.
One thing this study reminds us is that, generally speaking, it makes sense to assess the relationship between cholesterol (or any other factor) and overall risk of death rather than individual conditions. It should also remind us that having a cholesterol level above 5.0 mmol/l is not a cause for concern, and may in fact be a cause of celebration.
1. Petursson H, et al. Is the use of cholesterol in mortality risk algorithms in clinical guidelines valid? Ten years prospective data from the Norwegian HUNT 2 study. J Eval Clin Pract. 25 Sept 2011 [Epub ahead of print]