It improves alertness, energy and, sometimes, moods. But it also can make the heart race and keep you up at night. So is coffee good or bad? Wake up and smell the latest research about that cup of joe:

• The perks: A significant number of recent studies indicate coffee has an array of health benefits. After analyzing data on 120,000 people over an 18-year period, researchers at Harvard have concluded that drinking one to three cups of caffeinated coffee each day can reduce the risk of type 2 diabetes by several percentage points, compared with not drinking coffee at all. Other studies indicate coffee consumption decreases the risk of stroke, cardiovascular disease, colon cancer, liver cirrhosis, gallstones, skin cancer and Alzheimer's disease, although more research is needed. Regular coffee drinkers have up to 80 percent lower risk of developing Parkinson's disease, says a study published in 2004 in the American Journal of Epidemiology.

• The risks: Coffee during pregnancy has been linked to lower birth weight and an increased risk of miscarriage and stillbirth, although there is no proof at this point that caffeine causes miscarriages, according to the American College of Obstetricians and Gynecologists. Diabetics also are urged to switch to decaf because caffeinated coffee exaggerates blood sugar response to meals. In excessive amounts, coffee can cause nervousness, jitters and abnormal heart rhythms. In some, it can also increase blood pressure. Although studies investigating a relationship between higher cholesterol levels and coffee have yielded conflicting results, it's believed that in some people, drinking excessive amounts might cause elevated cholesterol levels (especially if it's unfiltered French press or boiled coffee).

• Coffee virgins: Some studies suggest that drinking coffee may act as a trigger for heart attack among some infrequent coffee drinkers. The potential risk seems to dissipate in chronic coffee drinkers. Non-coffee drinkers who suddenly start using caffeine also have shown a pronounced increase in blood pressure, but after a week or so, the effect fades, according to the Nurses' Health Study, a long-running research project with 238,000 participants.

• The bottom line: For many people, a moderate amount of coffee -- two to four cups per day -- is probably safe, according to the Mayo Clinic. But heavier amounts -- say, four to seven cups -- per day may result in difficulty sleeping, nervousness, irritability, nausea, a fast or irregular heartbeat or muscle tremors. To learn more, check out Vanderbilt University's Institute for Coffee Studies, which investigates the health effects of coffee consumption, at www.vanderbilt.edu/ics.

Get Smart appears every other week, and offers a quick overview of health and medical topics in the news. Got a question or suggested topic? E-mail jmailander@MiamiHerald.com.

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