The World Health Organization estimates that influenza affects three to five million people every year.

BBC: Flu drug 'shows promise' in overcoming resistance

That's a whole lot of agony, and it affects three times as many women as men, largely because the ups and downs of our hormones seem to make us more susceptible, according to Andrew Charles, M.

CNN: Stop that splitting headache

Anosmia, an inability to smell, affects an estimated three million people in the UK and can be present from birth.

BBC: James Paget Hospital smell clinic 'victim of own success'

Osteoporosis affects one in three women over the age of 50.

BBC: NEWS | Health | Complex cause for brittle bones

The doctors behind Health eHeart also hope to help solve the riddle of what causes atrial fibrillation, an irregular heartbeat that can lead to stroke and now affects more than three million Americans.

WSJ: Heart Disease Study Aims to Chart Risk of Heart Attacks, Strokes in Real Time