Selenium

Why athletes need more selenium in their diet

The orthodox view in sports nutrition is that while athletes may need more nutrients than their sedentary counterparts, they don’t need to worry because athletes eat more food to fuel their training, which automatically supplies any extra needs. However, new research into the essential trace mineral selenium suggests that this view may be over-complacent.

A French study on 118 well-trained athletes examined how closely selenium intake related to energy expenditure, and also whether the amount of selenium consumed was sufficient to maximise the effectiveness of the selenium-dependent enzyme glutathione peroxidase, a key enzyme in the body’s antioxidant defence systems, which helps to neutralise highly reactive and damaging free radicals.

All the athletes completed seven-day food diaries and activity records, which were then carefully cross-referenced. Blood samples were then taken on day 8 and examined for selenium content.

As expected, those athletes with the highest daily energy expenditure had the highest selenium intakes (because they were eating more food to refuel, food which contained selenium). The researchers also found that only 2.6% of the athletes had levels of blood selenium that were deemed to be clinically low.

More disturbing, however, was the finding that 23% of the men in the study and 66% of the women had selenium intakes below two-thirds of the French RDA (recommended daily amount), while the plasma selenium concentrations of all but the most elite athletes were below those needed to maximise the activity of the protective glutathione peroxidase enzyme. Moreover, the relationship between blood selenium and energy expenditure was not linear – ie eating 50% more food did not result in 50% higher blood selenium levels. The researchers concluded that selenium requirements are increased in athletes, but are not linearly related to energy expenditure.

These findings are important for two reasons:

  1. Many athletes may not be consuming even the basic amounts of selenium for their needs, let alone the optimum amounts required to protect cells from the higher throughputs of oxygen and consequent potentially damaging free radical production associated with sport activity;
  2. Simply relying on a larger overall calorie intake to provide extra selenium may not be a foolproof strategy.

Selenium, it seems, is another mineral that athletes neglect at their peril!

Biofactors 2005; 23(1):45-55