Our 16-year-old son is training with a professional football team. He is a central defender and will constantly have to head away long balls. My wife has been told this could lead to dementia in later life. Is this true?

That worry was settled a few years ago. It may have been true of the old leather balls that got heavier because they absorbed water during the game, but it doesn't apply to the newer, lighter, non-absorbent balls. The theory was that repeated headers produced mini-episodes of concussion, leading to cumulative brain damage. The lighter ball rules this out. So your son can continue to head the ball without worry.

I've had a bad chest infection that my doctor calls a flu-like illness. I'm itching to get back to work, but she says I should stay off for at least another week. Is she afraid I am still infective to others, or is she more concerned about me?

She is thinking of you. We all know about absenteeism - people who take time off when they aren't sick - but 'presenteeism' (ie, going to work when you should be off sick) can be as bad. Around three years ago, a study of Whitehall civil servants found that 17% of those who were unhealthy and should have taken time off didn't. They had twice as many heart attacks (and were twice as likely to die from them) as similarly unhealthy people who did take time to convalesce. Bosses who pressurise people to come to work at all costs are following a bad strategy in the long term.

· Do you have a question for Dr Smith? Email doctordoctor@theguardian.com