With this in mind, a team from the University of Alaska Fairbanks, US, has studied levels of mercury and antioxidants in sled dogs in villages on the Yukon River, which crosses the entire state of Alaska.

"Most of the Yukon River is inaccessible by vehicle," Kriya Dunlap told environmentalresearchweb. "Remote villages along the river are inhabited by Alaskan Natives who rely heavily on subsistence foods and lifestyles and have had historically low incidence of many age-related disparities. [This] is rising with the use of westernized diets and customs."

Sled dogs tend to eat the same foods as people in the region – chiefly salmon, but also black bear, moose and pike – so studying them can indicate how changes in foods are likely to affect humans.

"Sled dogs make a unique model for studying subsistence living," said Dunlap. "Aside from similarities in key biochemical pathways [to people], and their large homogenous sample size, they also eat almost exclusively subsistence foods for parts of the year. Salmon is a major part of the diet in the summer months when the salmon are running."

Dunlap and colleagues examined 12 Alaskan huskies from each of four villages along the Yukon River – Russian Mission, Galena, Rampart and Fort Yukon – and also 12 dogs at a reference kennels in Salsha, Alaska. The village dogs had been fed on a diet containing at least 90% local cooked salmon for the last two months, while the kennel dogs had eaten meat-based commercial dog food that did not contain fish or fish products.

The kennel-based dogs had significantly higher levels of antioxidants than the other animals. Mercury concentrations in the village dogs ranged from 139 to 15,800 ng/g; the researchers found that the dogs' blood contained fewer antioxidants when samples of their fur had higher mercury levels. They say this indicates that mercury can reduce antioxidant levels and potentially cause dietary insufficiency; some of the health benefits of the subsistence diet may be due to its high level of antioxidants and omega-3 fatty acids.

According to Dunlap, salmon act as contaminant pumps by migrating for long distances without eating and bringing pollutants from the ocean upriver. On the journey to their freshwater spawning grounds the salmons' body composition changes dramatically. "As salmon migrate they are mobilizing their fat and protein stores," said Dunlap. "While salmon who have migrated a great distance may have shed some of their contaminant burden, they may also have less healthy polyunsaturated fatty acids. It is really a risk/benefit relationship, with antioxidants being only one health index."

Although information from the study has been shared with the mushers (sled-dog owners) who participated, Dunlap says it is premature to make diet recommendations based on these findings. "The level of mercury found in this study, even at the highest kennel, is considered safe by the EPA [US Environmental Protection Agency] and the health benefits of eating salmon far exceed the risks," she added.

Now the scientists will continue to develop sled dogs as a research model for subsistence living. They plan to look at other health indices such as inflammation, which is involved in the progression of many diseases. They'll also sample a large number of salmon for direct analysis.

The scientists reported their work in Environmental Research Letters (ERL).