Many topics in nutritional science attempt to show the effects of a nutrient on health. These studies share a large confound — when we adjust the quantity of a nutrient in a subjects diet the health effects vary. This variance depends on which nutrient (e.g. unsaturated fat or refined carbohydrate) replaces dietary fat. Nutritional studies of coffee have a unique opportunity in this regard. It can be added with no modifications to subjects diets, as coffee without additives contributes virtually zero energy.
The objectives of this article are to assess the current claims around regular consumption of coffee. Can coffee be considered a beneficial component in one’s diet?
Coffee has a long history of numerous health claims, including: increased or decreased risk of cardiovascular disease; protective effects against Parkinson’s disease, type 2 diabetes, and cancer; effective appetite suppressant for weight management; increased or decreased all-cause mortality.
One of the challenges behind affirming or rejecting these claims is the variance in coffee products. Coffee contains drastically different concentrations of hundreds of compounds depending on the brewing method, processing, species (Coffea arabica or Coffea robusta), roasting process, growing environment, etc.
Coffee is rich in antioxidants which have been popularly claimed to be beneficial for health. However, the “antioxidant hypothesis” — that a diet rich in antioxidants lowers chronic disease risk — is unproven (1).
Unfiltered coffee contains diterpene molecules. These molecules have been shown to raise serum triglycerides, total cholesterol, and LDL-C, but not HDL-C (2–4). This effect has been shown in both randomized controlled trials and epidemiological studies and is a known risk factor for cardiovascular disease. Coffee consumers with hyperlipidemia appeared to be more sensitive to cholesterol-raising effects across all reviews. However, filtered coffee contained negligible quantities of diterpenes.
Caffeinated coffee has been shown to acutely raise blood pressure (5).
Epidemiological studies appear to support a non-linear dose-response relationship to cardiovascular risk — moderate coffee consumption is associated with a lower risk of CVD and heavy coffee consumption has no association (6–8). Other studies found that the risk association was inconclusive or negligible (2, 3). This non-linear relationship is discordant with the two risk factors mentioned above.
In addition, there appears to be an inverse association between coffee consumption and depression, which is a known factor for cardiovascular disease (8).
There does appear to be an inverse association between caffeine and Parkinson’s disease (9, 10). Some claims have been made that compounds in coffee (e.g. niacin) aside from caffeine protect against Parkinson’s disease but studies have found no relation (10).
Claims on an increased risk of cancer from coffee consumption appear to be unsupported from the current reviews. While there are many types of cancer, the current evidence suggests either no relationship or a minor inverse relationship for studied cancers. (11–13). Some studies have found a significant inverse association between coffee consumption and colorectal cancer risk (14).
There appears to be a plausible link between coffee consumption and a reduced risk of type 2 diabetes (15–17). This link is independent of caffeine, although the evidence is preliminary at this point.
Preliminary evidence suggests that coffee may assist in weight loss through multiple mechanisms such as increased satiety, increased activity level, and attenuation of glucose absorption (18, 19). These effects are minute however, and coffee consumers who use additives such as sugar, milk, or cream, have a higher daily energy intake than non-consumers (19).
The long-standing popular claim that coffee is bad for your health appears to be unfounded. Epidemiological studies support a reduction in mortality from coffee consumption (11, 20, 21).
The evidence for coffee consumption leading to better health is fragile. Studies find either inconclusive results or only minor reductions in risk. Reviews of epidemiological studies do strongly support further study of the topic, including potential causal mechanisms for some statistically significant positive health benefits. Coffee consumption appears to be safest if the consumer does not have hyperlipidemia or hypertension. The ideal brewing method is up for debate — paper filters significantly reduce the concentration of diterpene molecules which have been shown to negatively affect serum lipids. Conversely, these molecules may be the mechanism behind the potential neuroprotective effects of coffee independent of caffeine.
Concerns over negative health effects from coffee consumption appear to be generally unfounded given the current body of evidence. Evidence suggests coffee is safe to drink, but claims towards positive health benefits are exaggerated.
Note: I had to remove the titles from these studies due to the word limit, I would encourage you to read through some though.
- http://www.ncbi.nlm.nih.gov/pubmed/15153272
- Coffee Consumption and Serum Lipids http://aje.oxfordjournals.org/content/153/4/353.full.pdf
- Coffee consumption and cardiovascular health http://www.ncbi.nlm.nih.gov/pubmed/23990273
- The effect of coffee consumption on serum lipids http://www.ncbi.nlm.nih.gov/pubmed/22713771
- http://ajcn.nutrition.org/content/84/4/682.long
- Long-Term Coffee Consumption and Risk of Cardiovascular Disease http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3945962/
- Coffee, caffeine, and coronary heart disease. http://www.ncbi.nlm.nih.gov/pubmed/18089957
- http://www.sciencedirect.com/science/article/pii/S0735109713026016
- http://www.ncbi.nlm.nih.gov/pubmed/20182023
- http://jama.jamanetwork.com/article.aspx?articleid=192731
- Coffee and Health: A Review of Recent Human Research http://www.tandfonline.com/doi/full/10.1080/10408390500400009
- http://www.ncbi.nlm.nih.gov/pubmed/24668519
- http://carcin.oxfordjournals.org/content/35/2/256.long
- http://www.ncbi.nlm.nih.gov/pubmed/22694939
- http://www.ncbi.nlm.nih.gov/pubmed/25599007
- http://www.ncbi.nlm.nih.gov/pubmed/16399494
- http://www.dmsjournal.com/content/1/1/6
- http://ajcn.nutrition.org/content/84/4/682.long
- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2864136/
- http://www.ncbi.nlm.nih.gov/pubmed/23465359
- http://www.ncbi.nlm.nih.gov/pubmed/25156996