New York, Dec 23 (IANS): Seasonal sun exposure -- a key factor in the body's natural ability to make vitamin D -- plays a substantial role in how well people do after weight loss surgery, new research has found.

Results of the study reveal interplay among vitamin D status, seasons, geography and surgery outcomes, said lead researcher Leigh Peterson from Johns Hopkins University in Baltimore, Maryland, US.

Specifically, the researchers found that patients undergoing bariatric surgery in the US during winter -- January to March, the time of lowest vitamin D levels -- fared worse than patients who had procedures in the summer.

Similarly, patients having surgery in the north seemed to have more complications than those in the south.

"Sun exposure is critical in the synthesis of vitamin D, so the notion that people living in less sunny northern states may suffer from vitamin D deficiency is not surprising," Peterson noted.

"What is remarkable is how closely sun exposure, vitamin D and surgical outcomes were linked," Peterson said.

For the study, researchers reviewed records of more than 930,000 bariatric operations performed in the US between 2001 and 2010.

The researchers found that people from the northern part of the country were more likely to spend a few extra days in hospital.

The researchers noticed, adverse outcomes, such as non-healing wounds, wound infections, wound separation and delayed wound healing, clustered in colder seasons marked by less sunshine.

For example, more than twice as many patients experienced delayed wound-healing complications in the winter -- 349 patients -- than in the summer -- 172 patients.

The study appeared online in the journal Obesity Science & Practice.