Cholesterol is found in both high density and low density lipoproteins, called HDL and LDL. HDL, or "good cholesterol," has a higher proportion of protein to triglyceride and cholesterol than does LDL, or "bad cholesterol." Having too much LDL or too little HDL can lead to heart problems. HDL levels can fluctuate widely, depending on the season, activity levels, medical conditions or even the lab where you get your testing done.
Lab Variations
It's important to have an accurate reading of cholesterol levels, because doctors use these results to prescribe medicine or recommend dietary changes. Big fluctuations in HDL and other cholesterol numbers might reflect when or where you are tested. You need a fasting blood test to determine your HDL, LDL and triglyceride numbers. According to pediatrician Bill Sears, "Several things can affect the accuracy of cholesterol blood tests: fluctuations in weight, changes in diet, pregnancy and excessive alcohol intake. The most accurate results are obtained when your weight has been stable for at least two weeks and you are eating your usual diet." The laboratory you choose also might have an effect on your numbers. Equipment, testing protocols and even what is considered a normal reference range can vary from lab to lab.
Seasonal Changes
HDL and other blood cholesterol levels are higher in the fall and winter than they are in the spring and summer, according to a 2004 study reported in the Archives of Internal Medicine. The study concluded that much of the variation is due to a difference in blood plasma volume, which is often higher in the warmer months. The study also found that women and those who already had high cholesterol levels were more likely to experience these fluctuations.
Exercise
Moderate exercise on a regular basis can increase HDL levels. Men who participate in exercise programs intense enough to get their heart rate to at least 75 percent of maximum can dramatically increase their HDL levels. Women who exercise regularly also show improved HDL scores, but the intensity of exercise needed varies between pre- and post-menopausal women. Not surprisingly, HDL is more likely to increase significantly in those who start with a lower HDL number.
Medical Conditions
While unusual, some people have medical conditions or take medications that might affect HDL levels. For example, one study showed that people with homozygous familial hypercholesterolemia, or HFH, may show a big drop in HDL after taking high doses of atorvastatin drugs, though these effects are short-lived. Another study, "Disturbance of Serum Lipid Metabolism in Active Renal Failure," published in 1981 in "Renal Failure," found that some people with acute renal failure experienced a significant decrease in their HDL levels, but once the medical condition was stabilized, the HDL levels also recovered.
References
- Ask Dr. Sears: Controlling Your Cholesterol
- Archives of Internal Medicine: Seasonal Variation in Serum Cholesterol Levels
- University of New Mexico Department of Health, Exercise & Sports Sciences: A Review of the Impact of Exercise on Cholesterol Levels
- American Heart Association: Magnitude of HDL Cholesterol Variation After High-Dose Atorvastatin Is Genetically Determined at the LDL Receptor Locus in Patients With Homozygous Familial Hypercholesterolemia
- Informa Healthcare: Disturbance of Serum Lipid Metabolism in Acute Renal Failure
