There is much debate about the health effects of caffeine, and whether these effects are primarily positive or negative. Caffeine, particularly in coffee, has been studied closely to determine where it may be of benefit, and where it may cause undesirable effects.
Caffeine is a stimulant. In healthy adults this means that the effects of caffeine will tend to make one feel more alert, less sleepy, and will temporarily boost metabolism. Yet because it is a stimulant, one of the effects of caffeine is letdown a few hours after intake. If a person drinks coffee or other caffeinated beverages all day, they are unlikely to feel this drop in mood or alertness. The person who drinks caffeinated beverages in the morning only, may find themselves feeling more tired as the day progresses.
For some people, the stimulating effects of caffeine can cause jumpiness, increased irritation, or poor sleep. Individual response greatly varies. Some groups of people should avoid caffeine altogether. Those with heart rhythm problems, a likelihood of developing arrhythmias, or who have panic or anxiety disorders will probably not benefit from the effects of caffeine. In fact, consumption can exacerbate these disorders.
Another one of the negative effects of caffeine is that it is mildly addictive. Those who consume caffeine on a regular basis are subject to caffeine withdrawal if they abstain for a day or so. This usually presents as a terrible headache, and excessive sleepiness. Side effects of caffeine withdrawal tend to last for two to three days.
Noting the headache caused by caffeine withdrawal led researchers to study the effects of caffeine on those with persistent headaches or migraines. Research found that caffeine is actually of great benefit to those with migraines or frequent headaches. Over the counter medications like Excedrin® combine aspirin, caffeine and acetaminophen and are thought to be most effective in treating headaches. Frequently migraine sufferers take a caffeine supplement at the first signs of an oncoming migraine. In this way the effects of caffeine are beneficial.
Effects of caffeine have also been studied in pregnant women. It is currently thought that moderate use of caffeine, perhaps a cup to two cups of coffee a day, is unlikely to have an effect on the growing child. It is also unlikely to affect fertility or cause miscarriage. Some of these studies have been criticized because the population of pregnant women has undergone changes. Women are now likely to have children later in life, which may affect both fertility and miscarriage rate. So the debate still rages on the effects of caffeine in the pregnant woman.
Caffeine does pass into breastmilk and may affect the nursing child. Excessive caffeine in breastmilk may cause irritability or sleepiness. Other children seem unaffected by moms consuming caffeine. Most pediatricians advise breastfeeding mothers to consume no more than one cup of coffee a day to avoid unwanted effects of caffeine in a nursing child.
The effects of caffeine on women in general have been studied extensively to see if caffeine intake increases risks for certain cancers. In 1990, three studies concluded that breast cancer risk is not increased by caffeine. Further studies in the 1990s also concluded that ovarian cancer risk does not increase in caffeine users. Caffeine is also not indicated in the development of osteoporosis.
Because caffeine is a mild diuretic, effects of caffeine for those who do not have sufficient fluid intake can cause mild dehydration. If one regularly indulges in caffeinated beverages, fluid intake of water or juices should be increased. Physicians urge people to especially monitor caffeine intake during very hot weather, or when traveling to hot climates. The effects of caffeine in such conditions are likely to be more harmful than beneficial.