Even though I have been studying diabetes and helping people with diabetes to live better with it for over thirty years, I still get surprised constantly when a new study challenges my firmly held assumptions! One message that has been pushed down our throats for over twenty years at least is that the lower your blood glucose levels are the better. Yes, we are told, it can be a nuisance pushing your blood glucose levels closer and closer to normal because you run the risk of feeling weird or even passing out from a too low blood glucose (hypoglycemia) and you may need to check your blood glucose more often and may gain weight but over the long haul you will stay healthier if your average blood glucose levels are kept as close to normal as you can. It is a simple message to push. Organizations like the American Diabetes Association have pushed the message hard. All the big pharmaceutical companies who make drugs that help push your blood glucose lower and lower have a vested interest in pushing the message that "lower is always better, and even lower is better still!" But some recent research studies have challenged this simple message.
The ACCORD trial is a large randomized controlled research trial carried out in many different medical centers around the world. In the study 6,779 people with type 2 diabetes were randomly assigned to a "standard" approach to lowering their blood glucose where they aimed to get their HbA1c between 7-8% and keep it there or to an "intensive" approach where they tried to get their HbA1c as low as they could get it and keep it there (You can read the full study results in the journal Diabetes Care 33:721-727, 2010). These subjects had had their diabetes for several years and many of them had had heart disease already (angina, or a heart attack) or had risk factors for heart disease (like high blood pressure or a history of smoking or heart disease in their family). After about five years of follow up the standard therapy group achieved an average HbA1c of 7.5% whereas those in the intensive treatment group kept their HbA1c at 6.4%.
The surprising results of the study were that after 4-5 years of follow up there were more deaths in the intensive therapy group than in the standard therapy group. This was even more noticeable in people who had had very poor HbA1c levels to begin with and in people who had worse nerve damage (neuropathy) at the start of the study.
Another study published in the Lancet this year (Currie, CJ, et al. Lancet 375:481-489, 2010) looked at over 50,000 people with type 2 diabetes treated in general practice in the United Kingdom. The researchers followed what happened to those people after they had their diabetes treatment intensified by having an extra blood glucose lowering pill or insulin added to their treatment. As you would expect their HbA1c levels dropped lower after the new treatments were added. But when they looked to see how those people did in the next few years they found that those whose HbA1c levels stayed high were more likely to die and that those with a lower HbA1c did better... but only up to a point. It was bad to have a HbA1c of over 9.0% for example. Those who got it down to 8.5% did better and those at 8.0% or 7.5% did better still. However, if the new treatment pushed the HbA1c down below 7.0% the outcomes started to get worse with more people dying if their HbA1c was at 6.5% and even worse if it was 6.0%.
So what does this mean for you? There is no doubt that high blood glucose levels (HbA1c over 9.0%) are bad for your long term health and working to bring it down is a good thing to do. However, how low to push it is more complicated. I think it depends on what type of diabetes you have, how long you have had it, what your average blood glucose levels (HbA1c) have been for the past few years and whether or not you have risk factors for heart disease. For people with type 1 diabetes or people with type 2 diabetes who have always had HbA1c levels that are below 8.0% and who don't have risk factors for heart disease then pushing to keep your HbA1c level down below 7.0% is probably a good thing to prevent long term problems from your diabetes. But if you have had heart disease (or have several risk factors for heart disease like smoking or having high blood pressure and high cholesterol) and if your HbA1c has often been above 8.0% in the past few years then these research studies suggest that a better target for you might be to keep your HbA1c around 7.5%
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