Persistent tiredness may be a symptom of depression, diabetes, heart disease or another serious condition and should be evaluated by a health-care professional. Occasional periods of low energy, however, are associated with a lack of sleep, added stress, poor diet, lack of exercise and overindulgence in alcohol or other drugs. Quick energy and endurance may also be desired to improve athletic performance. The safety and effectiveness of any supplement to boost energy naturally has not been proven by adequately controlled scientific studies.
Creatine
A natural nutrient and amino acid found in animal foods, creatine may enhance athletic performance by increasing phosphocreatine, a major source of muscular energy. Portuguese researchers R.R. Mendez and J. Tirapequi investigated creatine's effects and found that rapid energy, speed and power may increase as a result of taking creatine, especially for high-intensity, short-term tasks. The report, published in the June 2002 Archivos Latinamericanos de Nutricion, advises that the use of high doses of creatine for up to eight weeks and taking low doses of creatine for up to five years have not been associated with health concerns. The effects of creatine may be diminished or eliminated by caffeine consumption.
Green Tea Extract
Green tea contains caffeine, which is associated with a short-term increase in energy and alertness. Other substances in green tea extract, known as catechins, may help with weight loss. Tomonori Nagao and colleagues from Health Care Products Research Laboratories in Tokyo studied the effects of catechins on body fat. Healthy Japanese men were divided into two groups and matched for BMI and waist size. The 12-week double-blind study gave each group a single bottle of oolong tea daily. One group's drink contained green tea extract with 690mg of catechins. The control drink contained only 22mg of catechins. Results were published in the January 2005 issue of the American Journal of Clinical Nutrition. The study found that body weight, BMI and waist circumference were lower than controls in men who received green tea extract.
Ginseng
Panax ginseng root, also known as Asian or Korean ginseng, is an ancient traditional remedy. Modern westerners use ginseng supplements as a stimulant. Ginseng contains nutrients such as calcium, choline, fiber, folate, iron, magnesium, manganese, phosphorus, potassium, zinc, thiamin, niacin, pantothenic acid and vitamin C. Medline Plus states ginseng may be effective for improved male sexual function, and there is evidence to support the belief that ginseng sharpens mental acuity and reaction times. Other possible effects include lowering of blood sugar. Ginseng supplements should not be used by people with hypoglycemia, hypertension, arrhythmia, asthma or insomnia. Ginseng is not recommended for use during pregnancy or breastfeeding.
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