The increasing use of caffeine as an additive in many foods and drinks has attracted considerable scrutiny from regulators and researchers. So have proposals to add the stimulant to such items as toothpaste or body sprays.
The Institute of Medicine last month spent two days hosting a forum on the potential health hazards of caffeine consumption at the request of the U.S. Food and Drug Administration, which in turn is trying to decide if limits need to be imposed on how much of the stimulant can be added to various products.
That may take some time and more research. The conference revealed many gaps in scientific research into how caffeine delivered in new ways -- such as in gum -- may affect a person's total daily intake, and how various doses may affect athletes, young people and others.
There have been some reports of deaths tied to consumption of energy drinks. The government says the products were linked to some 20,000 emergency-room visits in 2011.
Right now, the FDA only regulates caffeine that's added to a food, drug or other product, but not when it occurs naturally. So, for instance, caffeine in pain relievers and cold pills is labeled, but the amounts contained in chocolate in candy bars are not. Neither are the amounts of caffeine included in energy drinks sold as dietary supplements.
Although people have been consuming caffeine for thousands of years, no one can be entirely sure what amounts to a safe or unsafe dose of caffeine, although for most people, the drug's effects are mild and transient. Definitive answers on the possible benefits caffeine can bring are also far off.
At the extreme, scientists have set a toxic dose at somewhere around 10,000 milligrams. The average 8-ounce cup of coffee has 80 to 125 milligrams. A moderate dose is considered two to four cups a day.
Consuming 500 to 600 milligrams a day is enough to cause effects such as insomnia, nervousness, upset stomach, fast heartbeat or muscle spasms in many people.
The stimulant can be dangerous for people with heart-rhythm problems and high blood pressure, among other medical conditions.
And an estimated 20 percent of the population is thought to be caffeine-sensitive, to the point that just a few milligrams can produce the jitters or other problems.
On the flip side, the compound's effects on the nervous system may benefit short-term memory. Several studies have found a decreased risk of liver disease among those who consume a four-cup dose of caffeine on a daily basis.
Some studies have linked an increase in caffeine consumption with a higher risk of miscarriage among pregnant women. The FDA advises pregnant women to avoid or limit caffeine intake.
Even if you want to monitor your caffeine intake from drinks, it can be difficult.
The amount can vary depending on how long or by what process a beverage is steeped or brewed. And since the effects of caffeine we ingest are usually felt within about 45 minutes, hot drinks that are sipped may have a different impact than cooler beverages that might be gulped or chugged.
Half the caffeine a person takes in gets eliminated in five or six hours, but men and smokers process it faster than women and nonsmokers.
Women on oral contraceptives break it down more slowly than others, while menstrual cycles may also play a role. Some studies have found lower estrogen levels in women who drink more than 200 mg a day.
For those who want to track consumption, color-changing caffeine test strips can tell whether a drink really is decaffeinated. The strips generally can distinguish a high-test brew from a low-test one. Federal regulations require that a product sold as decaf has to have 97.5 percent of caffeine removed, but consumer testing has shown that can leave 3 milligrams to dozens of milligrams in a serving.
But a new sensor kit, developed by scientists in Singapore and South Korea, applies a lab-on-a-disc technology to detect caffeine across a traffic-light-style spectrum of doses.
The sensor device, dubbed Caffeine Orange, works by exposing a drink sample to a green laser pointer, which then triggers a chemical reaction that lights up the sensor. High caffeine concentrations from coffee or energy drinks turn the sensor display reddish-orange, while teas and decaf drinks show up as yellow and green.
The new device was described in a paper published in July in the journal Scientific Reports.
(Contact Scripps health and science writer Lee Bowman at BowmanL@shns.com.