A large study of Canadian adults has questioned the role of HDL in maintaining good health - suggesting it's merely a marker of a healthier lifestyle
Guidance on dietary choices and cholesterol levels in particular has been somewhat unreliable, with a great deal of backtracking and contradictory findings from different studies. As they are insoluble, cholesterol and fatty acids are transported in the blood by different lipoproteins, which vary in size and function. LDL (low density lipoprotein) has been demonised as a major cause of atherosclerosis and cardiovascular disease, while HDL (high density lipoprotein) is often considered the 'good' form that scavenges excess cholesterol. In reality, it's not quite so simple. Both perform essential biological functions. Because of this lingering uncertainty around HDL's real value, a large study of almost 632,000 people above 40 in Canada sought to unravel the influence of HDL levels on mortality risk.
A mixed picture
One finding from the study was that those people with the lowest HDL levels were most likely to die from many causes, including both heart disease and stroke. However, those with the highest HDL levels were actually more likely to die of non-cardiovascular causes. Those in the middle appeared to be better protected against multiple diseases.
"Many people know that HDL is the 'good' cholesterol. But they may not know that the medical community is moving away from the idea that we've got to raise low HDL"
So what does this mean?
Because low HDL levels were linked with additional disease such as cancer, the researchers theorised that HDL was merely a marker of other factors. Those with low HDL were typically of a poorer background, were more regular smokers, and more likely to be diabetic, obese and have high blood pressure. It seems likely that low HDL is a signpost of a wide range of detrimental influences, which has a negative impact on more than just cardiovascular disease risk. HDL itself may have little beneficial effect when it comes to CVD. This echoes other similar findings from research in which HDL levels were boosted, and little beneficial effect was recorded. Furthermore, gene variants associated with HDL levels have not been connected to disease risk either - suggesting that HDL has a fairly small influence alone.
Rethinking HDL's role in disease
Perhaps the most stark finding of the study is that high HDL was not protective and in fact correlated with increased risk of non-cardiovascular disease. Those with a happy medium of HDL performed best of all, and while the researchers do believe that a healthier general lifestyle is likely to boost HDL levels, this is a bit of a red herring. There are so many other factors going on here in cardiovascular disease especially, that HDL's protective role appears to have been vastly inflated and is not backed up with evidence.
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