Caffeine is a stimulant that acts on the central nervous system to temporarily increase alertness and ward off drowsiness. It's a vital part of coffee, certain sodas and energy drinks. For a long time, researchers have been interested in caffeine and its possible effects on various physiological phenomena, but its effect on cholesterol, if it has an effect, appears to be mild at best. Instead, it is another compound, terpene, which is a major ingredient of some caffeinated beverages, that appears to raise cholesterol.
Cholesterol is a type of fatty substance that plays a critical role in the production of bile acids, steroid hormones and vitamin D. It also is a major component of the flexible membrane that surrounds and protects every cell in your body. Cholesterol is not soluble within blood, so the liver must process and package it within molecules called lipoproteins — combinations of proteins and fats — for transportation throughout your body. Low-density lipoproteins, or LDL, transport cholesterol to its destination, but high levels can damage arteries and cause heart disease. High-density lipoproteins, or HDL, transport cholesterol back to the liver for excretion. For this reason, experts often call HDL a "good" cholesterol.
Researchers have noticed a link between caffeinated beverages and cholesterol levels for decades, especially to coffee drinking before 1975. A 1994 study published in the journal "Psychosomatic Medicine" by a group of researchers from the Duke University Medical Center suggested that the consumption of caffeinated beverages was associated with two risk factors for coronary heart disease: high LDL cholesterol levels and a high ratio of total cholesterol to HDL levels. LDL levels always are higher than HDL levels, but an exceptionally high ratio indicates that HDL cholesterol is far too low in comparison.
Caffeine itself might not be to blame for increased cholesterol levels. According to Michael J. Klag, the vice dean for clinical investigations at John Hopkins University School of Medicine, oils called terpenes might be the culprit. Klag and his colleagues noticed this trend in 2001 when they reviewed dozens of studies and discovered that the rise in cholesterol was almost a unanimous product of unfiltered coffee, which leaves both caffeine and terpenes after processing, rather than filtered coffee, which leaves only the caffeine. Another study pinned the blame on a specific type of terpene called cafestol that might hijack a receptor in the intestines that regulates cholesterol. The researchers from Baylor College of Medicine found that consuming five cups of unfiltered French press coffee a day, which amounts to 30 milligrams of cafestol, over a period of four weeks raised blood cholesterol by 6 percent to 8 percent. This suggests that cafestol and not caffeine causes the change in cholesterol.
Merely decaffeinating coffee is not enough to significantly influence cholesterol levels. Filtering coffee is the important factor. Fortunately, filtered coffee has become the norm throughout the United States, greatly reducing the consumption of the terpenes typically found in association with caffeine. However, researchers have not ruled out the possibility that filtered coffee might raise cholesterol by a very small amount, nor have they dismissed other caffeinated beverages such as soda on the same grounds.