The Safety of Ingested Caffeine: A Comprehensive Review

A prospective analysis of risk factors for Alzheimer's disease was a major objective of the Canadian Study of Health and Aging, a nationwide, population-based study. Of 6,434 eligible subjects aged 65 years or older in 1991, 4,615 were alive in 1996 and participated in the follow-up study. All participants were cognitively normal in 1991 when they completed a risk factor questionnaire. Their cognitive status was reassessed 5 years later by using a similar two-phase procedure, including a screening interview, followed by a clinical examination when indicated. The analysis included 194 Alzheimer's disease cases and 3,894 cognitively normal controls. Increasing age, fewer years of education, and the apolipoprotein E epsilon4 allele were significantly associated with increased risk of Alzheimer's disease. Use of nonsteroidal anti-inflammatory drugs, wine consumption, coffee consumption, and regular physical activity were associated with a reduced risk of Alzheimer's disease. No statistically significant association was found for family history of dementia, sex, history of depression, estrogen replacement therapy, head trauma, antiperspirant or antacid use, smoking, high blood pressure, heart disease, or stroke. The protective associations warrant further study. In particular, regular physical activity could be an important component of a preventive strategy against Alzheimer's disease and many other conditions.

Caffeine is consumed by over 80% of U.S. adults. This review examines the effects caffeine has on cognitive and physical function, since most real-world activities require complex decision making, motor processing and movement. Caffeine exerts its effects by blocking adenosine receptors. Following low (∼40mg or ∼0.5mgkg(-1)) to moderate (∼300mg or 4mgkg(-1)) caffeine doses, alertness, vigilance, attention, reaction time and attention improve, but less consistent effects are observed on memory and higher-order executive function, such as judgment and decision making. Effects on physical performance on a vast array of physical performance metrics such as time-to-exhaustion, time-trial, muscle strength and endurance, and high-intensity sprints typical of team sports are evident following doses that exceed about 200mg (∼3mgkg(-1)). Many occupations, including military, first responders, transport workers and factory shift workers, require optimal physical and cognitive function to ensure success, workplace safety and productivity. In these circumstances, that may include restricted sleep, repeated administration of caffeine is an effective strategy to maintain physical and cognitive capabilities.

To review the effects, adverse consequences, and extent of energy drink consumption among children, adolescents, and young adults. We searched PubMed and Google using "energy drink," "sports drink," "guarana," "caffeine," "taurine," "ADHD," "diabetes," "children," "adolescents," "insulin," "eating disorders," and "poison control center" to identify articles related to energy drinks. Manufacturer Web sites were reviewed for product information. According to self-report surveys, energy drinks are consumed by 30% to 50% of adolescents and young adults. Frequently containing high and unregulated amounts of caffeine, these drinks have been reported in association with serious adverse effects, especially in children, adolescents, and young adults with seizures, diabetes, cardiac abnormalities, or mood and behavioral disorders or those who take certain medications. Of the 5448 US caffeine overdoses reported in 2007, 46% occurred in those younger than 19 years. Several countries and states have debated or restricted energy drink sales and advertising. Energy drinks have no therapeutic benefit, and many ingredients are understudied and not regulated. The known and unknown pharmacology of agents included in such drinks, combined with reports of toxicity, raises concern for potentially serious adverse effects in association with energy drink use. In the short-term, pediatricians need to be aware of the possible effects of energy drinks in vulnerable populations and screen for consumption to educate families. Long-term research should aim to understand the effects in at-risk populations. Toxicity surveillance should be improved, and regulations of energy drink sales and consumption should be based on appropriate research.