The man, who was in his forties and wearing shorts and trainers, has not yet been identified. He was discovered in "severe distress" by passers- by on a remote beach at Fairlight Glen, near Hastings, on Wednesday.
Rescuers believe that he fell asleep in the sun as temperatures hit the high eighties on one of the hottest June days on record.
A spokesman for the Conquest hospital in Hastings, where the body was taken, refused to comment on the man's death or the condition of his body until the results of the post-mortem examination are known.
Paramedics trekked for 30 minutes through the Hastings country park and along the beach to reach the isolated spot after the alarm was raised at 7.30pm on Wednesday evening. The man was found to be in need of urgent medical attention and was evacuated further along the shoreline by the Hastings in-shore lifeboat to a spot where he could be transferred to an ambulance and taken to hospital. He was declared dead on arrival.
Prolonged exposure to strong sun can be dangerous and lead to sunstroke when the body's heat-regulating mechanism breaks down, leading to severe dehydration in some cases, and possible heart and lung failure.
Dr Meg Price, a member of the British Medical Association's Dermatology Committee and a consultant dermatologist at Brighton Healthcare Trust, said: "Acute sunburn is more than burning the skin. I would not say that just sunburn by itself will kill a person, but the victim may dehydrate, meaning that the blood pressure will drop. This can put a tremendous strain on the heart."
t A council has called its winter gritter lorries into service to spread sand across roads as scorching summer sun melts the tarmac. Highland Regional Council is spending pounds 6,000 spreading the sand in an attempt to limit damage to roads and vehicles.
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