It鈥檚 a common complaint of marathon runners and soldiers alike. Overdo the exercise and you fall victim to illness, particularly chest infections. Now it seems that quercetin 鈥� a flavonoid found in fruits, berries and tea 鈥� may protect them.
For the past few years, has been sponsoring studies of quercetin in the hope that it could protect US troops. 鈥淒uring missions, soldiers are running around for two or three days with heavy packs on. They don鈥檛 eat or sleep, and infections are as much of a problem if not a more serious issue than injuries,鈥� says David Nieman at Appalachian State University in Boone, North Carolina, who led the research.
He gave 40 male cyclists either 1 gram of quercetin a day 鈥� equivalent to eating 100 apples 鈥� or a placebo, for three weeks. During this time, the cyclists spent a three-day period training at maximum intensity for 3 hours each day. 鈥淏y the time they were done they were just wasted,鈥� Nieman says.
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Two weeks later, nine of the cyclists in the placebo group had suffered chest infections, compared with just one in the quercetin group (Medicine and Science in Sports and Exercise, ).
Tests showed that the cyclists taking the supplement had high levels of quercetin in their blood. Lab studies have previously shown that quercetin can bind to viruses and bacteria and stop them replicating; this is what Nieman believes was happening in the cyclists to stop them getting sick.
Nieman also found the cyclists had reduced levels of IL-8, a chemical that helps mediate the immune response to antigens, suggesting that quercetin may also be influencing the immune system in some way (Journal of Applied Physiology, ).
He is now looking at whether quercetin could benefit people suffering from high mental stress, who are also at greater risk of infection. He also hopes to establish the minimum amount of quercetin needed to achieve a protective effect. The average American typically eats around 107 milligrams of flavonoids 鈥� which are polyphenols 鈥� per day. There are no apparent side effects of boosting the intake, says Nieman.
Nieman鈥檚 studies 鈥減rovide important new evidence regarding the health benefits of polyphenols in general and quercetin in particular鈥�, says Holden MacRae at Pepperdine University in Malibu, California. Last year he showed that quercetin improved cycling time-trial performance by around 3 per cent, when given in combination with antioxidants, in a small study of elite male athletes (International Journal of Sport Nutrition and Exercise Metabolism, vol 16, p 405).
Sprint or Endurance?
How come some people can run for hours without exhaustion, while others burn out? The answer may be a gene variant which makes muscle cells work more efficiently. Mice engineered to lack a protein called a-actinin 3, which is usually found in fast muscle fibres responsible for explosive bursts of power, were able to run for 33 per cent longer on average than mice with a-actinin 3.
a-actinin 3 is usually made by the ACTN3 gene. However, around 20 per cent of people carry a variant which cannot produce the protein. Previous studies had suggested that sprint athletes rarely carried this ACTN3 variant, while it was more common among endurance athletes.
To investigate how a-actinin 3 could influence muscle function, Kathryn North at the University of Sydney, Australia, and her colleagues engineered mice to lack a-actinin 3. As well as being able to run for longer, the muscle fibres of the mice had more mitochondria 鈥� the 鈥減ower houses鈥� of cells (Nature Genetics, ). 鈥淭hese findings suggest that a-actinin 3 is associated with baseline changes in muscle metabolism,鈥� says North.
Moreover, when North鈥檚 team analysed the DNA surrounding ACTN3 in humans with the variant gene, they found that it was highly conserved 鈥� suggesting that it had been positively selected for during evolution. Since the ACTN3 variant is more common in Asians and Europeans, North suggests that it may have helped people adapt to harsher conditions when they were migrating out of Africa. 鈥淏eing more metabolically efficient may have provided an advantage during times of famine,鈥� she says.
