History provides a few pointers. According to the Bible, the tallest man was Goliath at "six cubits and a span", which, depending on whose conversion you believe, puts him somewhere between nine and a half and 11ft tall. Sadly though, the Bible was not peer-reviewed, so Goliath must be disqualified.

The tallest man on record is Robert Wadlow, an Illinois man who died at 2.71m (8ft 11in) in 1940 at the age of 22. The record may not stand for much longer, however. This week, Leonid Stadnyk, a 33-year-old living in a remote village in Ukraine, hit the news as the world's tallest living man. At 2.54m (8ft 4in), he is just 17cm short of Wadlow's record. In the past two years, he has grown 30cm.

Like Wadlow, Stadnyk owes his extraordinary height to a tumour on his pituitary gland. The tumour churns out growth hormone but it's a secondary effect that leads to the runaway growth that doctors call acromegalic gigantism.

Normally, the growth of our bones is limited by our sex hormones. A good burst of sex hormones at the right time tells the ends of our bones to stop growing. In acromegalic gigantism, as the tumour grows, it destroys cells in the pituitary gland that stimulate the release of sex hormones. The bones, therefore, never get the signal to stop growing.

But surely there must be a limit to a person's height? John Wass, a specialist in acromegalic gigantism at the University of Oxford, reckons it would be impressive to survive for long if you grew taller than 9ft.

First, high blood pressure in the legs, caused by the sheer volume of blood in the arteries, can burst blood vessels and cause varicose ulcers. An infection of just such an ulcer eventually killed Wadlow.

With modern antibiotics, ulcers are less of an issue now, and most people with acromegalic gigantism eventually die because of complications from heart problems. "Keeping the blood going round such an enormous circulation becomes a huge strain for the heart," says Wass.