At least five tourists have died in Greece and others are missing as temperatures soar, according to media reports. “Many tourists underestimate the effort associated with a walk in direct sunlight,” Athens cardiologist Thomas Giannoulis says. “The temperature can rise to 37 degrees in the shade and easily up to 60 degrees in the sun.” This increases the risk of dehydration and heatstroke. “And the danger rises the older a person is,” Giannoulis says. All of those who have died or gone missing are tourists aged from 55 to 80. The first was a 67-year-old British journalist who went missing on S…