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There are many phenomena which cycle with the seasons. In the Spring, thunderstorms rumble across mid-west countrysides. Summer brings waves of sunbathers to coastal beaches. Autumn is signaled by the leaves of many trees turning fiery red. And in the winter, your cholesterol goes up. Surely this is not as exciting as the other examples, but it can have a far more immediate personal impact on your health.

It has been well documented that cholesterol levels tend to increase in the winter and lower in the summer. This elevation is more profound in women and in people with already elevated cholesterol.

Common wisdom dictates that this increase is simply due to most people being less active in the winter months. But as with much common wisdom, the real answer is actually a bit more complex. Scientists and doctors have searched for hard evidence as to the primary cause of seasonal variation in cholesterol levels. Is it mostly a function of changes in internal body metabolism, or are outside factors such as diet and exercise more important? So far, the definitive answer has been: we don't know.

This phenomenon could be important when making critical decisions on whether a lipid lowering medication should be started after a period of dietary lifestyle change. Patients could get discouraged if, despite intense adherence to a low cholesterol diet, their level stayed the same. This could happen if they started dietary measures in late summer or fall and lipid levels were rechecked again in the middle of winter. It would appear to the person taking the medication that it was not having any effect, when in fact it was holding off the otherwise expected seasonal rise.

It is suggested that the changes in cholesterol could be due to a change in blood volume that occurs during the warmer months. A greater blood volume could result in a lower concentration of cholesterol without changing the bodies' total cholesterol. Essentially, the blood cholesterol levels become more dilute.

Evidence for a lifestyle effect in seasonal cholesterol levels is more straightforward. Weight loss and physical activity can lower cholesterol levels. People are often less active in the winter and often gain their winter fat stores. Less activity and more body fat can easily lead to a transient increase in cholesterol levels.

Even more interestingly, it is not known if these seasonal variations in cholesterol levels translate into higher risk of heart attack or stroke.

Recent studies have shown a seasonal variation of about 4 points higher in winter for men and 5.4 points higher in winter in women. These are relatively small changes and would not likely result in changes to prescribed therapy. However, in patients with cholesterols starting out higher in summer, over 240 mg/dl, the change was much more dramatic. Variations of 11 points in men and 18 points in women in this higher risk group were found. This possibly could influence decisions in therapy.

So what is the end result of knowing that cholesterol levels can fluctuate by season? It is important to work closely with your doctor to lengthen the time you take to modify your lifestyle using dietary and exercise intervention before starting cholesterol controlling medications. Cholesterol levels fluctuate with many outside factors and it is important to create a very good baseline of levels before initiating long term therapy. As always, should you have further concerns about your cholesterol levels and how they can fluctuate naturally or be changed by your lifestyle, be sure to consult your doctor. Together you can make a plan for cholesterol control that is specific to you.

Learn more about this author, Erich Rosenberger M.D..
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