Is it true that it only affects postmenopausal women?

No, men are often also affected by osteoporosis. One third of all fractured hips and vertebrae due to osteoporosis occur in men. The onset of osteoporosis in men is 10 – 15 years later than it is in women, largely because men have more bone mass to lose than women. Small, lean men are more prone to osteoporosis than heavy-set men. But the majority of people who suffer from osteoporosis are postmenopausal women.