Friday, August 23, 2013

Research finds ‘raised’ cholesterol to be associated with a reduced risk of death - Briffa


In the UK and Europe generally, it is recommended that levels of cholesterol in the blood should not be above 5.0 mmol/l (= about 190 mg/dl). We are given the impression that having levels above this puts us at increased risk of heart disease – a major ‘killer’. However, if this is true, it does not tell the whole story. Because while having a ‘raised’ cholesterol may be associated with an increased risk of heart disease, it might also be associated with a reduced risk of other conditions.
It is known, for instance, that higher levels of cholesterol are associated with a reduced risk of cancer. And even last week I wrote about some research which suggests that putting downward pressure on cholesterol levels increases the risk of death due to suicide, accidents and violence.

For these reasons, when assessing the relationship between any lifestyle factor and health, it pays to take as wider a view as possible. This is best done by focusing on the relationship the factor has with overall risk of death.

Such a study published recently in the Scandinavian Journal of Health Care makes for some interesting reading, I think [1]. Here, researchers assessed the levels of cholesterol and risk of death in almost 120,000 adults living in Denmark.

The researchers found that having higher than recommended levels of total cholesterol was associated with a reduced risk of death. For instance, in men aged 60-70, compared with those of total cholesterol levels of less than 5.0 mmol/l, those with total cholesterol levels of 5.00-5.99 had a 32 per cent reduced risk of death. For those with levels 6.0-7.99 mmol/l, risk of death was 33 per cent lower. Even in individuals with levels with 8.00 mmol/l and above, risk of death was no higher than it was for those with levels less than 5.0 mmol/l.

The results were similar for women too. In women aged 60-70, levels of 5.0-5.99 and 6.0-7.99 were associated with a 43 and 41 per cent reduced risk of death respectively.

In individuals aged 70 and over, the results were similar, except here, levels of total cholesterol of 8.00 mmol/l or more were associated with a reduced risk of death too (in both men and women).
Cholesterol in the blood stream is made up of two main types: LDL-cholesterol and HDL-cholesterol, dubbed ‘bad’ and ‘good’ cholesterol respectively. In this study, higher levels of LDL-cholesterol (above 2.5 mmol/l) were consistently associated with a reduced risk of death, irrespective or age or sex.

Together, these findings suggest that the current total cholesterol and LDL recommendations advised by doctors and other health professionals are way off beam. The authors of this study concluded that: “These associations indicate that high lipoprotein levels do not seem to be definitely harmful in the general population.”

Some have suggested that low cholesterol is a marker for ‘frailty’ in the elderly. However, this concept is contradicted by evidence finding that the association between low cholesterol levels and enhanced risk of mortality occurs in younger individuals too [2].

It has also been suggested the relationship between low cholesterol and enhanced risk of mortality is the result of ‘reverse causality’ i.e. that chronic conditions such as cancer can cause lowered cholesterol, rather than the other way round (sometimes referred to as ‘Iribarren’s hypothesis’).
However, evidence refuting this concept comes in the form of a long-term study which found that individuals with a low serum cholesterol maintained over a 20-year period had the worst outlook in terms of overall risk of death [3]. The authors of this study write: “Our present analysis suggests that this [Iribarren’s] hypothesis is implausible and is unlikely to account for the adverse effects of low cholesterol levels over twenty years.”

In the Danish study, the relationship between blood fats known as triglycerides and risk of death was also assessed. In women aged 50-60, higher triglyceride levels were consistently found to be associated with increased risk of death. This was somewhat true for women aged 60-70.

This does not mean that higher triglyceride levels cause heart disease – only that these two things are associated with each other. However, the major driver of triglyceride levels is dietary carbohydrate. And previous studies have found that swapping certain carbohydrates for fat in the diet is associated with an increased risk of cardiovascular disease [4,5].

All-in-all, I’d say this research should cause us to pause before recommending individuals aspire to current cholesterol recommendations. And, I think, we should be particularly wary about recommending that people adopt a lower-fat diet richer in carbohydrate to achieve these goals. There is at least some evidence which suggests that this is likely to do more harm than good.

1.  Association of lipoprotein levels with mortality in subjects aged 50 + without previous diabetes or cardiovascular disease: A population-based register study. Scandinavian Journal of Primary Health Care 2013;31(3):172-180
2.  Ulmer H, et al. Why Eve is not Adam: prospective follow-up in 149650 women and men of cholesterol and other risk factors related to cardiovascular and all-cause mortality. J Womens Health 2004;13(1):41-53
3. Schatz IJ, et al. Cholesterol and all-cause mortality in elderly people from the Honolulu Heart Program: a cohort study. Lancet 2001;358(9279):351-5
4. Jakobsen MU, et al. Intake of carbohydrates compared with intake of saturated fatty acids and risk of myocardial infarction: importance of the glycemic index. Am J Clin Nutr 2010;91(6):1764-8
5. Jakobsen MU, et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr 2009;89(5):1425-32
Read the complete article here.

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