People have grown taller over the last century, with South Korean women shooting up by more than 20cm on average, and Iranian men gaining. 16.5cm. A global study looked at the average height of 18-year-olds in 200 countries 1914 and 2014.The results reveal that while Swedes were the tallest people in the world in 1914, Dutch men have risen from 12th place to claim top spot with an average height of 182.5cm. Larvian women. Meanwhile, rose from 28th place in 1914 to become the tallest in the world a century later, with an average height of 169.8cm.James Bentham, a co-author of the research from Imperial College, London, says the global trend is likely to be due primarily to improvements in nutrition and healthcare. “An individual’s genetics has a big influence on their height, but once you average over whole populations, genetics plays a less key role,” he added.A little extra height brings a number of advantages, says Elio Riboli of Imperial College. “Being taller is associated with longer life expectancy,” he said. “This is largely due to a lower risk of dying of cardiovascular（心血管的）disease among taller people.”But while height has increased around the world, the trend in many countries of north and sub-Saharan Africa causes concern, says Riboli. While height increased in Uganda and Niger during the early 20th century, the trend has reversed in recent years, with height decreasing among 18-year-olds.“One reason for these decreases in height is the economic situation in the 1980s,” said Alexander Moradi of the Universith of Sussex. The nutritional and health crises that followed the policy of structural adjustment, he says, led to many children and teenagers failing to reach their full potential in terms of height.Bentham believe the global rtend of increasing height has important implications. “How tall we are now is strongly influenced by the environment we grew up in,” he said. “If we give children the best possible start in life now, they will be healthier and more productive for decades to come.”