Media playback is unsupported on your device Media caption Keith Richards on drugs and relationship with Mick Jagger

The Rolling Stone's autobiography reveals a lifetime of substance abuse. Why on earth hasn't it killed him?

His name is synonymous with rock 'n' roll excess, his memoirs detail a lifetime spent ingesting a Herculean quantity of illegal drugs and he only gave up cocaine, aged 62, after he split his head open falling from a tree while foraging for coconuts.

At 66, Keith Richards' continued survival is a source of widespread bafflement.

According to addiction expert Dr Robert Lefever, director of the Promis recovery centre in Richards' native Kent, there is only one possible explanation for his longevity: "He must have the constitution of an ox."

But Richards' own memoirs suggest he may have been more careful with his intake than his bacchanalian public persona implies.

The autobiography, Life, is candid about the scope of his notorious drug-taking during his lengthy career as the Rolling Stones' lead guitarist and co-songwriter.

"I used to walk down Oxford Street with a slab of hash as big as a skateboard," drawls a typical passage.

Richards describes hurtling around swinging London fuelled by speedballs, a cocktail of cocaine and heroin he refers to with his customary louche archness as "the breakfast of champions".

He claims that during the notorious Redlands raid of 1967, he allowed the police into his home in Sussex because he was under the misapprehension, as a result of copious quantities of LSD, that the officers were dwarves "wearing dark blue, with shiny bits and helmets".

The Answer Richards himself says he was more careful than his image suggests

But his constitution appears to have been particularly strong

The deaths of so many around him suggest that most people simply cannot cope with such a high intake

And although he gave up heroin in 1978 after being busted five times, he did not finally stop taking cocaine until 2006 after the coconut tree incident required him to undergo brain surgery.

Yet along the way he also managed to have the wherewithal to produce some of the greatest and most memorable rock albums of all time, inspiring generations as both a guitarist and a songwriter.

In his book, he acknowledges that his wealth allowed him to ingest a higher quality of substances than the typical drug user.

But he adds: "I was very meticulous about how much I took. I'd never put more in to get a little higher.

Image caption Keith Richards may have emerged from the 1960s intact, but Brian Jones (left) did not

"It's the greed involved that never really affected me. People think once they've got this high, if they take some more they're going to get a little higher. There's no such thing. Especially with cocaine.

"Maybe that's a measure of control and maybe I'm rare in that respect. When I was taking dope, I was fully convinced that my body is my temple."

The latter statement is one that few people would readily associate with Keith Richards, but then biographers of the the guitarist have always noted his tendency to shield his true inner self from public gaze by playing up to his outrageous image.

While the "Keef" of Redlands and other hellraising tales might be the one regularly represented in the media, less well-discussed is Keith Richards the antique book collector - a man who, in unguarded moments, has spoken fondly of his childhood love of public libraries, and who attempted to catalogue the thousands of volumes in his home according to the Dewey Decimal system.

Nonetheless, the sheer volume of harmful substances ingested by Richards over the years suggests his survival can hardly be explained by restraint, Dr Lefever notes.

WHO, WHAT, WHY? A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines

"Whether it's genetic or because he's built up a tolerance, he does seem to have an unusually resilient constitution," he adds.

But Dr Lefever warns: "It's not something you can take for granted. For every Keith Richards, there are many, many more who die."

Indeed, the writer and music journalist David Quantick points to the tragic examples of companions who could not keep up - such as Gram Parsons and fellow Stone Brian Jones - as evidence that Richards is simply made of sterner stuff than most ordinary mortals.

"It's almost as though others die so that Keith Richards may live," Quantick observes.

"Still, it's not as though any children are going to think he's a good example. Just look at him: He's got a face like a prune's wallet."