An entertaining video about coffee, apparently NOT from Starbucks or the Coffee Lobby – provided by a frequent Cafe’er.
Since I drink a large Dunkin’ Donuts coffee (2.5 cups) almost every morning and became hooked on coffee, espresso and regular, in 1981 when I moved to Palo Alto CA, I have often wondered about the health effects of coffee. To make matters worse (or better), I usually have two cups of caffeine-laden tea a day. I finally got an opportunity to look into this in the past week. Here is what I learned from reviewing a large body of clinical studies on the health effects of coffee. Everything stated below can be backed up with high level publications of clinical studies and systematic clinical reviews.
Printers’ Inc was the first Coffee House/Book store, just a few blocks from the Pauling Institute and Stanford University. This is where Becki and I hung out on Sunday mornings and where I wrote grant proposals and research papers before power books. We enjoyed the brainiacs and other interesting writers and readers that surrounded us there.
Coffee is a complex mixture of chemicals that provides significant amounts of caffeine and chlorogenic acid to the consumer. Unfiltered coffee such as boiled coffee or espresso coffee is also a significant source of cafestol and kahweol, substances discussed below which are associated with elevated cholesterol. These two latter compounds are removed during paper filtration of percolated coffee. Overall, there is little evidence of health risks and some evidence of health benefits for adults consuming moderate amounts of coffee (3–4 cups/d providing 300–400 mg/day of caffeine).
Impact of coffee drinking on risk of type-2 diabetes
Six out of nine prospective cohort studies found a significant inverse association between the risk of type-2 diabetes mellitus (DM) and coffee intake.
A prospective study of more than 17,000 Dutch men and women found that the risk of developing type-2 DM was 50% lower in those who consumed at least 7 cups of coffee daily compared to those who drank 2 cups or less.
In Finland, where coffee consumption is among the highest in the world, a study that followed more than 14,000 men and women for an average of 12 years found that men who drank at least 10 cups of coffee daily had a 55% lower risk of developing type-2 DM than men who drank 2 cups or less, while women who drank at least 10 cups daily had a risk of type-2 DM that was 79% lower.
In a cohort of more than 10,000 Finnish twins, those who consumed at least 7 cups of coffee daily had a 35% lower risk of type-2 DM than those who consumed 2 cups or less.
In a smaller cohort of Swedish women followed for 18 years, those who drank at least 3 cups of coffee daily had a risk of type-2 DM that was about 50% lower than the risk for those who consumed less than 2 cups daily.
The two largest prospective cohort studies to examine the relationship between coffee consumption and type-2 DM were the Health Professionals Follow-up Study (41,934 men) and the Nurses’ Health Study (84,276 women) in the USA. Men who drank at least 6 cups of coffee daily had a 54% lower risk of developing type-2 DM than men who did not drink coffee, and women who drank at least 6 cups of coffee daily had a 29% lower risk than women who did not drink coffee. A more modest inverse association between decaffeinated coffee consumption and the risk of type-2 DM was also observed in both men and women, suggesting that compounds other than caffeine may have protective effects. In contrast, tea consumption was not associated with type-2 DM risk in the Dutch or American cohorts.
Impact of coffee drinking on risk of Parkinson’s disease
Overall, the results of case-control studies suggest that coffee and caffeine intakes are inversely associated with the risk of Parkinson’s disease. Several large prospective cohort studies have also found inverse associations between coffee and caffeine intakes and Parkinson’s disease risk in men. A study of more than 8,000 Japanese-American men found that those who did not drink coffee were 3–5 times more likely to develop Parkinson’s disease over the next 24–30 years than those who drank at least 28 oz daily. Caffeine intakes from coffee and other sources were also inversely associated with Parkinson’s disease risk. Similarly, in the Health Professionals Follow-up Study, men who regularly consumed at least one cup of coffee daily had a risk of developing Parkinson’s disease over the next 10 years that was about half that of men who did not drink coffee. The consumption of tea and other caffeinated beverages was also inversely associated with Parkinson’s disease risk. In contrast, inverse associations between coffee and caffeine consumption and Parkinson’s disease risk over a 16-year period were not observed in the Nurses’ Health Study. Similarly, in the Cancer Prevention Study (CPS) II cohort of more than 500,000 men and women in the US, coffee consumption was inversely associated with Parkinson’s disease mortality in men but not women. The failure of prospective studies to find an inverse relationship between coffee consumption and Parkinson’s disease in women may be due to the modifying effect of estrogen replacement therapy.
Further analysis of the Nurses’ Health Study cohort revealed that coffee consumption was inversely associated with Parkinson’s disease risk in women who had never used postmenopausal estrogen, but a significant increase in Parkinson’s disease risk was observed in postmenopausal estrogen users who drank at least 6 cups of coffee daily. In the CPS II cohort, a significant inverse association between coffee consumption and Parkinson’s disease mortality was also observed in women who had never used postmenopausal estrogen, but not in those who used postmenopausal estrogen. Caffeine is largely metabolized by hepatic CYP1A2, and the use of postmenopausal estrogen replacement therapy has been found to inhibit CYP1A2-mediated caffeine metabolism.
Possible mechanism for the effect of caffeine in Parkinson’s disease
Recent research supports the idea that chronic caffeine consumption could reduce Parkinson’s disease risk. Parkinson’s disease is characterized by the degeneration of dopaminergic neurons in the substantia nigra at the base of the brain. Studies in animal models suggest that caffeine consumption decreases the risk of Parkinson’s disease by protecting against dopaminergic neurotoxicity. The effects of caffeine in the central nervous system are related to its activity as an antagonist of the A1 and A2A subtypes of the adenosine receptor. The expression of A2A-receptors in the brain is restricted almost entirely to the striatum, the target of the dopaminergic neurons that degenerate in Parkinson’s disease. Acute toxicity with the neurotoxin, MPTP, can induce Parkinsonism in humans. This story was well documented in the book The Case of the Frozen Addicts and memorialized in the Public Television series NOVA under the same title. Dr. William Langston (a former colleague of mine), the discoverer of the link between MPTP and Parkinsonism, developed a well-established animal model of Parkinson’s disease uses MPTP to induce dopaminergic neurotoxicity in squirrel monkeys that was extended to mice. Caffeine, at doses comparable to typical human exposures, has been found to attenuate MPTP-induced losses of striatal dopamine and dopamine transporter binding sites in mice. Specific A2A-receptor antagonists mimicked the effect of caffeine as did the absence of functional A2A-receptors in A2Areceptor knockout mice. At present, it is not known exactly how A2A-receptor blockade reduces dopaminergic neurotoxicity. Read the rest of this entry »