The Sweat Boost

We've known for years that moderate exercise boosts the immune system: Those who exercise just 30 minutes a day are more resistant to colds and recover more rapidly from the colds they get. But exercise, like personality, has a nuanced impact on immunity:

• When exercise is prolonged and too intense, immunity weakens and you are more likely to get sick. Marathoners are always fighting colds, and their defenses may stay down for weeks or months after a race.
• Sweat really is youth serum. It's no secret that the immune system weakens as we age, but an Iowa State study shows that exercising elderly mice get a boost in immune health so that they are more like the young. For anyone hoping to slow the aging of their immune system, moderate exercise helps.
• Tai Chi, originally developed by Taoist monks to promote healing, can prime our immunity. Combining movement, meditation and special breathing, the practice has been linked to lower risk of heart disease, fewer falls in the elderly, even changes in neurotransmitters and improvement in mood.
• While marathoners typically suffer lowered immunity, cyclers are exempt from the long-distance rule. A study has determined that one can ride a bicycle for long distances at moderate intensity without weakening the immune system or becoming more vulnerable to flu and colds.