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copied from: http://www.healthyeatingclub.com/in...ds/caffeine.htm
Many epidemiological and intervention studies have examined the actions of caffeine on human health. The findings are equivocal. We cannot say for certain that caffeine is linked to any health conditions, however, there is emerging evidence of a link with impaired insulin action, hypertension and feelings of stress. With the proliferation of caffeine containing soft drinks and food products, all of which are easily accessed by children, more research is needed to explore the effects of caffeine on human health.
Diabetes
Two studies this year reported that caffeine affects insulin action (Kiejzers et al., Diabetes Care 2002; Thong et al Diabetes 2002). The findings are not completely new, but the degree to which the action of insulin was reduced was surprising. Impaired insulin action is the key step in the development of adult-onset diabetes. Impaired insulin means the pancreas is forced to secrete more insulin to have the same effect till at some point the pancreas starts to fail, leading to the death of insulin producing cells.
In these studies the equivalent of five to six espresso coffees were given either as tablets or injections and the effectiveness of insulin fell by 15 to 50%. This is similar to the effect obesity has on insulin action (lowers insulin action by 40%). It is well known that exercise increases the effectiveness of insulin, but after the ingestion of caffeine, insulin action was impaired, even though the subjects had exercised for one hour (Thong et al., 2002). It is speculated that caffeine activates receptors (adenosine) in adipose tissue, increasing both the concentration of fatty acids in the blood (which in turn may impair insulin action) and blood pressure. Caffeine also increases the levels of the stress hormone adrenaline which may also impair the action of insulin.
So should we avoid coffee, especially if we have a family history of diabetes? These studies (and no other studies) have proven that caffeine causes the development of diabetes. However, with the proliferation of caffeine containing soft drinks, more research is needed to explore the effects of caffeine on insulin action.
Hypertension & Stress
In another study (Lane et al., Psychosomatic Medicine 2002) 500mg of caffeine in the form of two tablets (equivalent to 4-6 cups of coffee) was given on a certain day of the week. Caffeine was found to cause a slight but signifcant increase in blood pressure and subjects reported feeling more stressed on the day they took caffeine; they also had greater levels of stress hormones. People with conditions that are aggravated by stress or who have high blood pressure need to be conscious of the amount of coffee they drink; alternatively they could switch to decaffeinated coffee.
Heart disease
Drinking 6 cups of unfiltered plunger coffee a day may increase the risk of heart disease (Grubben et al. AJCN 2000; 71: 480-4) because blood homocysteine and cholesterol levels increased by 10% and triglycerides by 36%. Sesquiterpenes in coffee is removed by filtering and is known to increase blood cholesterol levels. Caffeine may also lower blood levels of vitamin B6 which may explain the effect on homocysteine. However, coffee contains potentially cardio-protective flavonoids which have been shown to be antioxidants. Filtered coffee in moderation (2-3 cups per day) is probably OK.
Sport
Coffee has been shown to release fat from fat cells and hence have a possible benefit in a weight control diet. Marathon runners will drink a cup of coffee before a race to prevent hitting the wall. The theory behind this is that glycogen, or sugars, are the primary source of energy in the muscles, whereas fat is used as a ‘back-up’ fuel. Once glycogen supplies are exhausted (after 2 hours of vigorous activity) fat comes more into play, but this is not as easily accessible. Caffeine before a race may release fat into the blood stream quicker and help ‘save’ glycogen so this does not run out suddenly, leaving a feeling of ‘hitting a wall’ (Vinson & Dabbagh; Nut Research 1998; 18 (6): 1067-75).
Caffeine content of tea and coffee
Green tea has as much caffeine as black tea. A typical eight-ounce cup of tea prepared from one tea bag brewed for three to five minutes contains 40 milligrams of caffeine, compared with 100 milligrams in a cup of brewed coffee. The caffeine content of tea can range from 20 to 90 milligrams a cup, depending on the blend of tea leaves, method of preparation and length of brewing time, whereas a cup of coffee may contain from 60 to 180 milligrams of caffeine. Decaffeinated tea, like decaffeinated coffee, has about 4 milligrams of caffeine per cup. Instant teas and prepared iced teas, which can be purchased with or without caffeine, may be too highly processed to contain phytochemicals.
In conclusion, coffee in moderation (2-3 cups per day) is probably not an issue for most adults.
If you would like to find out about 'caffeine' - its dietary sources and whether it is harmful of beneficial - read this good on-line summary by Choice Magazine May 2000
Many epidemiological and intervention studies have examined the actions of caffeine on human health. The findings are equivocal. We cannot say for certain that caffeine is linked to any health conditions, however, there is emerging evidence of a link with impaired insulin action, hypertension and feelings of stress. With the proliferation of caffeine containing soft drinks and food products, all of which are easily accessed by children, more research is needed to explore the effects of caffeine on human health.
Diabetes
Two studies this year reported that caffeine affects insulin action (Kiejzers et al., Diabetes Care 2002; Thong et al Diabetes 2002). The findings are not completely new, but the degree to which the action of insulin was reduced was surprising. Impaired insulin action is the key step in the development of adult-onset diabetes. Impaired insulin means the pancreas is forced to secrete more insulin to have the same effect till at some point the pancreas starts to fail, leading to the death of insulin producing cells.
In these studies the equivalent of five to six espresso coffees were given either as tablets or injections and the effectiveness of insulin fell by 15 to 50%. This is similar to the effect obesity has on insulin action (lowers insulin action by 40%). It is well known that exercise increases the effectiveness of insulin, but after the ingestion of caffeine, insulin action was impaired, even though the subjects had exercised for one hour (Thong et al., 2002). It is speculated that caffeine activates receptors (adenosine) in adipose tissue, increasing both the concentration of fatty acids in the blood (which in turn may impair insulin action) and blood pressure. Caffeine also increases the levels of the stress hormone adrenaline which may also impair the action of insulin.
So should we avoid coffee, especially if we have a family history of diabetes? These studies (and no other studies) have proven that caffeine causes the development of diabetes. However, with the proliferation of caffeine containing soft drinks, more research is needed to explore the effects of caffeine on insulin action.
Hypertension & Stress
In another study (Lane et al., Psychosomatic Medicine 2002) 500mg of caffeine in the form of two tablets (equivalent to 4-6 cups of coffee) was given on a certain day of the week. Caffeine was found to cause a slight but signifcant increase in blood pressure and subjects reported feeling more stressed on the day they took caffeine; they also had greater levels of stress hormones. People with conditions that are aggravated by stress or who have high blood pressure need to be conscious of the amount of coffee they drink; alternatively they could switch to decaffeinated coffee.
Heart disease
Drinking 6 cups of unfiltered plunger coffee a day may increase the risk of heart disease (Grubben et al. AJCN 2000; 71: 480-4) because blood homocysteine and cholesterol levels increased by 10% and triglycerides by 36%. Sesquiterpenes in coffee is removed by filtering and is known to increase blood cholesterol levels. Caffeine may also lower blood levels of vitamin B6 which may explain the effect on homocysteine. However, coffee contains potentially cardio-protective flavonoids which have been shown to be antioxidants. Filtered coffee in moderation (2-3 cups per day) is probably OK.
Sport
Coffee has been shown to release fat from fat cells and hence have a possible benefit in a weight control diet. Marathon runners will drink a cup of coffee before a race to prevent hitting the wall. The theory behind this is that glycogen, or sugars, are the primary source of energy in the muscles, whereas fat is used as a ‘back-up’ fuel. Once glycogen supplies are exhausted (after 2 hours of vigorous activity) fat comes more into play, but this is not as easily accessible. Caffeine before a race may release fat into the blood stream quicker and help ‘save’ glycogen so this does not run out suddenly, leaving a feeling of ‘hitting a wall’ (Vinson & Dabbagh; Nut Research 1998; 18 (6): 1067-75).
Caffeine content of tea and coffee
Green tea has as much caffeine as black tea. A typical eight-ounce cup of tea prepared from one tea bag brewed for three to five minutes contains 40 milligrams of caffeine, compared with 100 milligrams in a cup of brewed coffee. The caffeine content of tea can range from 20 to 90 milligrams a cup, depending on the blend of tea leaves, method of preparation and length of brewing time, whereas a cup of coffee may contain from 60 to 180 milligrams of caffeine. Decaffeinated tea, like decaffeinated coffee, has about 4 milligrams of caffeine per cup. Instant teas and prepared iced teas, which can be purchased with or without caffeine, may be too highly processed to contain phytochemicals.
In conclusion, coffee in moderation (2-3 cups per day) is probably not an issue for most adults.
If you would like to find out about 'caffeine' - its dietary sources and whether it is harmful of beneficial - read this good on-line summary by Choice Magazine May 2000
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