Caffeine

15 Feb

PART 1: is there any neural benefit (improved alertness, improved neuromuscular recruitment, etc) for an individual to ingest moderate amounts of caffeine prior to and/or during their activities? (consider moderate to be 300 mg or less)

Caffeine is a drug that enjoys social acceptance and wide spread use around the world with 80% or more of adults consuming it daily (Burke, 2008).  Ingestion of caffeine can enhance mood, cognitive function, reaction time, endurance, and tolerance of fatigue.  There is considerable evidence that caffeine may enhance exercise capacity and recovery from fatigue.  It has been found that the effects are mainly attributed to its central nervous system stimulating actions (Faidon, & Stavros, 2005).  Caffeine can be an effective ergogenic aid over a wide range of athletic activities, involving both aerobic and resistance types of exercise (Faidon, & Stavros, 2005).  It seems the effects are more pronounced for endurance exercise than for short-term exercise.  Caffeine ingestion has been shown to extend time to fatigue and improve aerobic endurance and in situations where fatigue generally occurs within 30-60min (Faidon, & Stavros, 2005).

As researched by M. Tarnopolsky there is evidence for an effect on both the central nervous system and the excitation-contraction coupling of skeletal muscle (Tarnopolsky, 2008).  Several studies have suggested caffeine can enhance contractile force during sub maximal, decrease the rate of perceived exertion, increase in the ability to recruit motor units during forceful contractions, and have an increase in motor unit firing rates and synchronization (Tarnopolsky, 2008).  These suggestions have not been backed by large case studies in the laboratory setting. 

It is interesting to note a number of studies involving comparisons between habitual users of caffeine and low/non-users have found that habitual caffeine users demonstrated tolerance to the thirst-inducing effects of caffeine but not to the performance enhancing or mood enhancing effects (Ruxton, 2008).  In these studies habitual users experience greater cognitive of mood effects compared with low or non-users, which is surprising as tolerance would be expected to decrease any effects (Ruxton, 2008).  It does appear that habitual use doesn’t diminish the ergogenic effects of caffeine. 

Performance benefits can be found with moderate caffeine intakes of 100mg or more when it is taken before and/or during exercise (Burke, 2008). It is possible that athletes will consume caffeine in a more targeted manner in relation to their sporting activities as compared to the average daily intake of another individual (Burke, 2008). The most important reason for athletes to use caffeine is probably its perceived ergogenic efficacy, but caffeine is also inexpensive, can be consumed in generally legal amounts, has little or no acute adverse health effects, and is socially acceptable (Faidon, & Stavros, 2005).

PART 2: for the healthy non athlete are there any risk factors for consuming moderate levels of caffeine daily (moderate = 300 mg per day or less).

Several case studies suggests that it is sensible to consume caffeinated beverages within certain limits to deliver benefits to cognitive function without compromising other areas of health (Ruxton, 2009).  Some possible reported side effects are: dizziness, anxiety, irritability, inability to focus, jitters, increased heart rate, and dehydration (Faidon, & Stavros, 2005).  These side effects have been observed sparingly in several researched instances (Faidon, & Stavros, 2005).
There is a common fear that ingestion of caffeine may cause fluid electrolyte imbalances during exercise, leading to dehydration, which could hamper performance.  But this fact has yet to be backed by a substantial study.  It is possible that caffeine could have an adverse effect on hydration, as it increases blood flow to the kidneys and inhibits the re-absorption of sodium, calcium and magnesium, thus causing us to expel more water (Ruxton, 2008).  It is plausible that an increase in urine output prior to competition and increased sweating during competition, paired with the lack of proper hydration before and during activities could lead to a dehydrated state.  However, a recent review of caffeine and hydration status found that there is little scientific evidence that caffeine intake impairs overall fluid status (Burke, 2008).

Caffeine is widely consumed from a variety of sources as part of a normal diet, as well as in specialized sports foods and supplements that may be used by athletes during training and competition (Burke, 2008).  The odds of encountering an athlete that has taken caffeine to enhance performance are probably very high, but it is settling to know healthy adults with moderate daily caffeine intakes are not at risk for adverse effects (Burke, 2008).

Reference:

Burke, Louise. (2008). Caffeine and sports performance. Applied Physiology and Nutritional Metabolism, 33, 1319-1334.

Ruxton, Carrie. (2008). The impact of caffeine on mood, cognitive function, performance and hydration: a review of benefits and risks. British Nutrition Foundation: Nutrition Bulletin, 33, 15-25.

Ruxton, Carrie. (2009). Health aspects of caffeine: benefits and risks. Nursing Standard, 24(9), 41-48.

Faidon, Magkos, & Stavros, Kavouras. (2005). Caffeine use in sports, pharmacokinetics in man, and cellular mechanisms of action. Critical Review in Food Science and Nutrition, 45, 535-562.

Tarnopolsky, Mark. (2008). Effect of caffeine on the neuromuscular system – potential as an ergogenic aid. Applied Physiology and Nutritional Metabolism, 33, 1284-1289.

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