Low levels of vitamin D have long been identified as an unwanted hallmark of weight loss surgery. (Representational Image)
Seasonal sun exposure - a key factor in the body's natural ability to make vitamin D - may play a substantial role in how well people do after a weight loss surgery, a new study has claimed.
Low levels of vitamin D have long been identified as an unwanted hallmark of weight loss surgery, researchers said.
The study at the Johns Hopkins University in US on more than 930,000 patient records shows interplay among vitamin D status, seasons, geography and surgery outcomes.
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," said Leigh Peterson, a nutritionist and postdoctoral research fellow at the Johns Hopkins Centre for Bariatric Surgery.
"What is remarkable is how closely sun exposure, vitamin D and surgical outcomes were linked," said Mr. Peterson, who led the research.
Researchers reviewed records of over 930,000 bariatric operations performed in the US between 2001 and 2010.
Overall, they report, post-procedural complications were rare, with fewer than 1 per cent of patients developing infections.
A more common outcome was spending a few extra days in the hospital, and this showed the strongest relationship with both season and geography.
The researchers found a disproportionate number of those who fared worse hailed from areas north of latitude 37 degree than areas south of it.
For example, areas north of latitude 37 degrees yielded almost 150,000 more patients with an extended length of stay - more than three days in the hospital - after surgery than areas south of that latitude.
Considering that more than 300,000 of the operations, or over one-third of the total in the study, led to extended hospitalisation, 71 per cent of these surgical complications occurred north of 37 degrees.
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, or 0.16 per cent of operations reviewed - than in the summer - 172 patients, or 0.07 per cent of operations reviewed.
The study was published in the journal Obesity Science and Practice.