Well that's the claim out of Finland where putting babies out to sleep in freezing temperatures has been occurring for generations.
The trend started in the 1940's when air quality and general conditions within the home were poor. Sending children outside was seen as a healthier alternative.
Scientists and mothers in Finland both agree that there are health benefits with babies also sleeping longer when placed outside to sleep. It must be said that the baby is wrapped up to ensure it is snug and warm with no risk of freezing.
It just goes to show how culturally different we all are with advice on baby welfare and sleeping. Anyone that claims to have all the answers is probably someone to avoid!
See this link for the full BBC article http://www.bbc.com/news/health-31539089