Athletes who cram in extra workouts over the holidays to avoid packing on extra pounds also need to take extra precautions to avoid getting sick, recent guidelines stress.
In some ways, athletes are just like the rest of us. They're more susceptible to colds and the flu when they get too little sleep or drink too much alcohol.
But the physical demands of regular, prolonged, high-intensity training and competition are associated with changes in the immune system that can make them more predisposed to illness than people who aren't athletes, said lead author of the guidelines, Martin Schwellnus of the University of Pretoria in South Africa.
"Sudden increases in training and competition load can increase the risk of illness," Schwellnus, a sports medicine researcher, said by email.
The picture is different for those of who are more like weekend warriors than elite athletes.
Routine, moderate-intensity physical activity can help protect people against colds and diseases that involve the upper respiratory tract, previous research has found. Recreational runners, for example, tend to get fewer colds when they stick to their running program.
Exercise can boost the production of immune cells that attack bacteria tied to respiratory problems and colds. During exercise and for a little while afterwards, people may have higher levels of immune cells circulating through the body, which can also help ward off illness.
But too much exercise can have the opposite effect.
With intense, long-term exercise, the body may produce more stress-related hormones. During exercise, the body makes two hormones, cortisol and adrenaline, that are associated with spikes in blood pressure and cholesterol levels and temporary weakness in the immune system.
The guidelines published in the British Journal of Sports Medicine follow a consensus statement from the International Olympic Committee on how athletes can prevent illness.
Some of the advice will sound familiar even to people who have never set foot in a gym.
For example, athletes should always clean hands and nose after sneezing and coughing and keep other people with these symptoms at a safe distance, the guidelines recommend. They should also regularly wash their hands with soap and water.
Another common cold prevention measure also holds true for athletes - avoid sharing drinking bottles, cups, cutlery or towels with other people.
And, like the rest of us, they should avoid excessive drinking and practice safe sex.
Athletes should also minimize contact with infected people, young children, animals and contagious objects, the guidelines emphasize.
When they compete abroad, they should only drink beverages from sealed bottles, avoid raw vegetables and undercooked meat, and wash and peel fruit before eating.
To avoid insect-borne diseases, they should wear clothing that covers their arms and legs during training sessions in tropical areas. They should also carry insect repellent, anti-microbial foam or cream and alcohol-based hand washing gel.
"International travel and prolonged flights are also associated with an increased risk of illness in athletes," Schwellnus said. "Modern day athletes are required to travel extensively in some instances."
More research is needed to determine the best criteria for clearing sick athletes to return to practice and competition, Schwellnus noted.
"All of this is important in athletes because illness, particularly infective illness, can predispose athletes to increased risk of medical complication during exercise and also reduce their exercise performance," Schwellnus added.