The beauty of this curve from Fletcher from his longitudinal study on working men in London in 1977, is its simple and succinct depiction of the effect of cigarette smoke on lung function. In 2013, we still don’t know why some lungs are susceptible to smoke and others not, and why not every smoker develops lung disease. However, loss of lung function and changes in lung dynamics precede the onset of symptoms and the diagnosis of disease (which remains underdiagnosed). Smoke-related damage to lung tissue can rarely be repaired and the loss of lung function is irreversible. The good news is that stopping smoking, at any point along the curve, markedly improves prognosis.

My first trek in the Himalayas, setting out from Gangtok in the Indian state of Sikkim reaching a height of 4200m, was a hard one. Rain, leeches, altitude sickness and extremely heavy legs which slowly struggled up the last stretch. Our small group included a retired couple from South Africa. Almost 70, carrying their own backpacks, outpacing us by day and fit enough in the evening to regale us with stories from mount Kilimanjaro to ice treks along the frozen rivers of Ladakh.

That’s the sort of old age to aspire to. And I’m guessing that would not be an easy task after 20 a day for 40 years.