Coffee and Health
Caffeine/Caffeine and heart disease / Caffeine and woman
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The amount of caffeine in a cup of coffee can vary greatly, depending on its origin or the composition of the blend, the method of brewing and the strength of the brew. Instant, or soluble, coffee generally contains less caffeine than roast and ground coffee, but may be consumed in greater volume. Robusta coffees have about twice as much caffeine as arabicas. A 'cup' is usually understood to contain 150 ml (5 oz in the United States) but an espresso may be as small as 40 ml.
The U.S. Food and Drug Administration gives the following ranges for caffeine contents:
(mg per 5 oz cup)
|Roast and ground|
LEVELS OF CAFFEINE CONSUMPTION
Caffeine is generally consumed in amounts less than 300mg per day, roughly equivalent to:
3-4 cups of roast and ground coffee
5 cups of instant coffee
5 cups of tea
6 servings of some colas or
10 tablets of some Painkillers
It has been suggested that the British consume more caffeine on average than Americans, but there are no large scale studies to support the observation. The nine, normal subjects recruited by Dr M.S. Bruce and his colleagues, as habitual caffeine users, for a study in London (reference below) were found to consume on average 428mg caffeine a day, with a range from 230mg to 670mg.
Customary caffeine consumption has been classified as follows:
Low caffeine users: less than 200mg per day
Moderate caffeine users: 200-400mg per day
High caffeine users: more than 400mg per day
Studies on caffeine and various health effects tend to look atmoderate? versus heavy? caffeine consumption. While there are no consistent definitions of consumption levels, moderate? is typically defined as up to 300-400 milligrams (mg) a day -- the equivalent of 3-5, 8 oz. cups. More than this is usually considered heavy? consumption.
While there continue to be areas of debate, the weight of scientific evidence indicates that coffee and caffeine as consumed in the American diet are safe and do not effect fertility or cause adverse health effects in the mother or fetus.
A 1980 FDA study, in which researchers fed rodents large amounts of caffeine via stomach tubes, prompted an advisory for pregnant women to avoid caffeine. However, as a result of a significant amount of criticism regarding how the study was conducted, a second study was undertaken. The follow-up study, in which rodents consumed high levels of caffeine in their drinking water, found no effect.
This second study allayed the concerns that were generated by the initial 1980 study. This was reflected by Leviton in his 1995 review, who noted that only two studies since 1986 have evaluated the relationship between coffee/caffeine consumption and birth defects. These studies, by Olsen and McDonald, show no significant increased risk of malformation in babies born to mothers who consumed the most coffee (eight cups or more). (10, 11)
The FDA continues to advise pregnant women to consume caffeine in moderation as ought to be practiced with other dietary habits.
While a 1992 study identified aslight? increased risk with coffee consumption (32), a 1995 study by Pastore and Savitz concluded [our] results do not support an association between caffeinated beverage consumption and pre-term delivery, as is true in most previous studies.? (13)
A 1993 study by Larroque, et. al., showed no association between the highest level of caffeine intake (more than 800 mg) and low birth weight once researchers controlled for factors including maternal age, smoking and alcohol consumption. (8) Additionally, a prospective 1995 study by Shu, et. al, concludedcaffeine consumption showed no relation to fetal growth, even among heavy consumers? (up to 800 mg/day), after controlling for alcohol and smoking. (9). These findings are in contrast to those of the 1991 study by Fenster, et. al., which linked heavy caffeine consumption (more than 300 mg/day) with increased risk for intrauterine growth retardation and low birth weight (33).
The authors of a 1995 paper (Alderete, et. al.) on caffeine intake and time to conception concludedwe found no decrease in fertility among coffee consumers even at more than three cups per day.? These findings refute those of an earlier study, Wilcox et. al, which suggested an association between decreased fertility and 100 mg or more of caffeine per day (34). The researchers acknowledged that the decrease could be attributable to confounding factors, such as exercise, stress and nutrition, which the study did not address. Confounding factors also were problematic in a 1993 study by Hatch and Bracken, which concluded that consuming increasing amounts of caffeine is related to increasing delays in time to conception. A commentary on this study confirmed the researchers' own concerns, however, that women who conceive quickly may reduce caffeine consumption even before they are aware they are pregnant because of a natural aversion to caffeine that occurs during pregnancy,? thereby creating the potential for bias (35).
In the late 1970s surgeon John Minton completed research suggesting a possible link between FBD and consumption of methylxanthines, a group of purine-based compounds that includes caffeine (36). However, a 1986 study of more than 3,400 women conducted at the National Cancer Institute found no relationship between FBD and caffeine intake (16). That same year, a review of nine major studies reported there islittle evidence to support the association between methylxanthine consumption and fibrocystic breast disease.? (17)
Some physicians have suggested that women with FBD may be particularly caffeine-sensitive. (37) However, an extensive literature review by Wolfrom and Welsch in 1990 concluded that reducing or eliminating methylxanthine consumption has no consistent beneficial effect on FBD symptoms. (36) A February 1995 commentary states thatby and large, today's doctors feel that stopping caffeine is not really necessary? to reduce or prevent symptoms of FBD. (38) However, if a patient feels that caffeine makes her breasts more tender at certain times of the month, she should limit caffeine consumption to a level she is comfortable with.
At the time Minton completed his research on FBD, some researchers believed that the incidence of breast cancer was higher in women with FBD. They assumed, therefore, that caffeine consumption could lead to increased incidence of breast cancer (39,40). In 1992, Graham, et. al. concluded thatcontrary to the suggestion of Minton, we found no [breast cancer] risk associated with drinking coffee or any other caffeine-containing beverage. To our knowledge, no large-scale epidemiological study has ever done so.? (20)
A 1997 study by Lloyd, et. al., found no association between lifetime caffeine consumption and bone changes or osteoporosis risk in postmenopausal women (31). The researchers studied women who were low, moderate and high caffeine consumers, and controlled for exercise habits and hormone replacement therapy use.
In a 1996 longitudinal study of 145 healthy, college-aged women (20-30 years old), researchers concluded that moderate caffeine intake (defined in this study as one cup of coffee per day) was not associated with significant reduction in rates of bone gain in women in the third decade of life (41). This was one of the first studies to examine the effects of caffeine on bone mass in young women, 30 years of age or younger, who continue to gain bone.
Several studies completed between 1990 and 1995 have identified a net loss of urinary calcium or bone in subjects with high caffeine intake (42-44); however, it is difficult to extrapolate the results of these studies to the general population because the studies did not carefully control for confounding factors and/or included subjects with exceptionally high caffeine intake.
Other recent studies have found either that moderate caffeine consumption has no effect on total bone density or that any potential effects can be prevented by consuming adequate calcium. (26)
A 1994 study by Barrett-Connor, et. al., found a significant association between caffeine consumption and decreased bone density only among women who did not drink at least one glass of milk per day during most of their adult lives. (22)
A 1995 analysis by Barger-Lux and Heaney concluded thatone glass of milk provides enough calcium to offset the negative effect of eight cups of caffeine-containing coffee...this equivalence highlights the fact that it is not so much that caffeine is a risk factor for osteoporosis; rather, it is inadequate intake of calcium which is the principal culprit and which allows other minor players, such as caffeine, to express their effects.? (29)
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