The link between coffee and cholesterol

Many people are taking steps to lower their serum cholesterol by eating less fat, switching to olive oil, and exercising regularly. They may even use skim milk instead of cream in their coffee to lower saturated fat. But what about the coffee itself? Some scientists suspect that coffee increases cholesterol levels but the data have been conflicting. To investigate this further, researchers at Johns Hopkins University performed a meta-analysis on some of the intervention studies conducted over the past 16 years. The results were recently published in the American Journal of Epidemiology.

Two researchers identified 14 English language studies conducted between 1985 and 1992 that met the criteria for analysis. All of them involved human subjects with random assignment to the intervention -- coffee being the only difference between the treatment and control groups.

The investigators reviewed each study and recorded the effect (if any) coffee had on serum lipid levels. They also noted the characteristics of the study volunteers such as age, sex, baseline coffee consumption, and lipid levels. Design differences between the studies were also compared, including sample size, length of the intervention, method of coffee preparation, and the amount of coffee consumed.

To calculate the combined effects of all the interventions, the researchers weighted each study based on the reciprocal of its total variance. If variances were not reported, they were calculated from other statistics that were provided.

Overall, the pooled estimates of total and LDL cholesterol were increased significantly with coffee by an average of 11.8 mg/dL (0.31 mmol/L) and 6.5 mg/dL (0.17 mmol/L). There was also a small effect on triglycerides (5.9 mg/dL, or 0.07 mmol/L), but none on HDL cholesterol. However, the cholesterol changes were strongest if the subjects had pre-existing hypercholesterolemia; total cholesterol rose by an average of 33.5 mg/dL (0.87 mmol/L) when these subjects were exposed to coffee. Studies using subjects with normal cholesterol levels had a smaller increase, 6.1 mg/dL (0.16 mmol/L).

The type and amount of coffee matters

There were several other factors that appeared to be important to the coffee-cholesterol link. A separate meta-analysis showed that how the coffee was prepared was the critical factor. Boiled coffee showed significantly greater increases in total and LDL cholesterol and trigylceride levels compared with filtered coffee. A multiple linear regression analysis demonstrated this as well. Another key factor was the total amount of coffee consumed, with six or more cups per day having the greatest influence on cholesterol levels.

Isn't coffee fat free?

Oils present in coffee like cafestol and kahweol are believed to be responsible for its effects on lipids. They may increase the formation of cholesterol by decreasing excretion of bile acids and neutral sterols. The amount of oils in a cup of coffee depends on the preparation method. Boiled or French-pressed coffee retain more oil than filtered or drip coffee, possibly explaining the meta-analysis findings that boiled coffee had a greater cholesterol-raising effect.

Coffee drinking is probably not a concern for most people

This is reassuring news for Americans, the majority of whom drink filtered coffee. However, in European countries boiled coffee is more common and therefore may be more of a factor for those trying to lower serum cholesterol.

When making recommendations to patients with elevated cholesterol levels it may be worthwhile to ask about their coffee drinking habits. If they drink a large amount of unfiltered coffee, switching to filtered coffee may be a helpful addition to the traditional heart-healthy diet.