On the morning of May 19, 1845, the Franklin Expedition set off on an ambitious voyage through the last unnavigated section of the Northwest Passage, a winding iceberg-ridden sea route connecting the Atlantic and Pacific through the Arctic Sea. Not one of the 129 crew survived.

Due to the scant bits of evidence left behind, the story of this fated crew has since become the stuff of legend and mystery. Historians and numerous other scientific studies have long-speculated that their deaths were due to exposure to the cold paired with lead poisoning from the solder used to seal up their cans of food. 

A team led by Russell Taichman, a dentistry professor at the University of Michigan, have used his expertise in oral health and medicine to try and piece together their final days.

At some point around September 1846, the two ships of the expedition, HMS Erebus and HMS Terror, became stuck in ice deep within the Canadian Arctic Archipelago. Notes left by the crew explain that many of them survived for two years, living off their supplies of tinned food while their numbers slowly diminished, including Captain John Franklin who died in June 1847. By April 1848, the remaining crew decided to walk towards the Canadian mainland.

In the new study published in the journal Arctic, the researchers used accounts left by the Inuits who came across the struggling crew as they made thier journey. The Inuits reported that the men appeared horrifically thin and the mouths of some of them were hard, dry, and black.

This pointed Taichman's team towards the diagnosis of Addison's disease, a rare condition where the adrenal glands stop working. People with the condition have trouble regulating their sodium levels and therefore their fluid balance, leading them to become dehydrated and unable to maintain their body weight even if food is available. Distinctive signs and symptoms of the disease include weight loss, darkened skin, darkened lips, and darkened gums – more or less exactly like what the Inuits reported.

"In the old days, the most common reason for Addison's in this country was TB [tuberculosis]," Taichman said in a statement. "In this country now, it's immune suppression that leads to Addison's."

The study authors say there’s no doubt that the crew also developed scurvy and lead poisoning. However, ultimately these other unpleasant experiences weakened them to the point that they were struck with the final nail in the coffin – Addison's disease.

“Scurvy and lead exposure may have contributed to the pathogenesis of Addison's disease, but the hypothesis is not wholly dependent on these conditions," Taichman added. "The tuberculosis-Addison's hypothesis results in a deeper understanding of one of the greatest mysteries of Arctic exploration."