Caffeine's Stimulatory Effects Can Aggravate Some Medical Conditions.
Caffeine's effects on the body may aggravate chronic diseases. My colleagues and I at Duke and others around the world have shown in carefully controlled research studies that consumption of even moderate caffeine consumption raises blood pressure, increases the levels of circulating adrenalin in the blood, and exaggerates how much glucose and insulin rise after a meal. For healthy people, these effects may have little impact on health. But for those people with high blood pressure or type 2 diabetes, these effects of caffeine can make management of the chronic disease more difficult. Research has also shown that caffeine makes life feel more stressful, perhaps because caffeine exaggerates the adrenalin responses to stressful events in daily life. People who feel "stressed out" might benefit from eliminating caffeine from the diet.
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Who among us takes caffeine in pill form? The argument Dr. Lane offers, that caffeine consumption is "bad" for Diabetics may not actually apply to brewed coffee consumption. The 10 Diabetic test subjects from his Duke University report published in 2008 replaced their normal coffee consumption with caffeine pills. The testing was limited and didn't test actual coffee consumption. Please read more about the test process and results here:
http://diabetes.webmd.com/news/20080128/caffeine-risks-may-rattle-diabetics
There's much more evidence on the side of moderate coffee & tea drinking being beneficial to preventing Type 2 Diabetes. A broad test including more than 7,000 subjects was conducted several years ago defining usage in this area. (This test didn't include those with Diabetes.) Please see the ADA report here:
http://www.diabetes.org/diabetes-research/summaries/greenberg-coffee-diabetes.jsp
After reading both reports, we might infer that while caffeine alone, provided in pill form, has some negative affect on postprandial glucose levels in Diabetics, brewed coffee may actually be beneficial to preventing Diabetes in otherwise healthy people.
As brewed coffee was not tested by Duke University, Dr. Lane's assertion can only be used to argue that straight caffeine pills are not good for Diabetics.
The question of caffeine harm from brewed coffee and tea should be answered by weighing in on all the elements of the total substance, not just one element. Perhaps the good in brewed tea and coffee outweighs the bad of the caffeine to create a perfect balance.
It is very difficult for me to believe that moderate caffeine consumption can be harmful to an otherwise healthy person. Of course if someone has the blood pressure issues and other conditions you mentioned such as levels of circulating adrenalin, glucose and insulin levels, etc., they should naturally do everything in their power to avoid anything that will exacerbate these conditions.
Naturally, some people might be more susceptible to the effects of caffeine than others. We each need to know ourselves and take responsibility for our own lives. I don't feel that there should be one answer to this question which applies to evryone. However, for a normal healthy individual,moderation in caffeine consumption as with all other aspects of their life should be the rule.
http://www.ific.org/publications/brochures/caffeinebroch.cfm
I appreciate the reference to increase glucose and insulin in diabetics who drink caffeine, but is there any data on changes on morbidity and mortality associated with caffeine rather than changes in lab values?
Regarding glucose and insulin in type 2 diabetes, there is not yet evidence on relationships to morbidity and mortality of diabetic patients. Experimental studies that demonstrate physiological effects should stimulate research in the clinical implications. However, cross-sectional or longitudinal studies of health outcomes may not answer the question. Coffee drinking is a self-selected habit and those who are moderate to heavy consumers may be less sensitive to caffeine effects. Until we learn whether quitting caffeine improves diabetes or not will we know how clinically important this laboratory findings are.