As scientists across the Bay Area work diligently toward a cure for autism, the solution might be right outside their labs, streaming in through the windows.

UC Berkeley biology professor Bruce Ames and post-doctoral fellow at the Children’s Hospital Oakland Research Institute Rhonda Patrick discovered that vitamin D helps produce three brain hormones that affect social behavior. One of the hormones, serotonin, is alarmingly scarce in autism patients, leading researchers to believe that sunlight could be the vital cure to the behavioral syndrome.

Though scientists have previously noted the relationship between vitamin D and autism, the new research, published Feb. 20, highlighted the link between vitamin D and serotonin, thus confirming and explaining what were first only speculations as to the causes of the disorder.

“The more we dug, the more we were sure our theory was right, because it explained so much,” Ames said.

Data has thus far been mostly correlative, according to Patrick. The new findings, she said, form the “missing link” by providing a mechanism to relate the hormones. The mechanism explains that vitamin D is converted to a steroid hormone, which activates the gene that converts amino acids to serotonin in the brain.

“The ‘how’ is, of course, very important,” said John Cannell, executive director of the Vitamin D Council, who is not related to the study but published a paper last year proposing a correlation between vitamin D and autism levels. “It’s fine and good to have a theory, but unless you can explain how it works, the theory has not a lot of validity.”

The study’s mechanism goes even further, analyzing gut inflammation, common among autism patients. While the vitamin D hormone helps increase serotonin levels in the brain, it inhibits the production of serotonin in the gut. According to researchers, high levels of serotonin, which can lead to inflammation, may be caused by a lack of vitamin D.

Still, the serotonin deficiencies in the brain and excesses in the gut can be prevented by ensuring that young children and expectant mothers both maintain adequate levels of vitamin D through sunlight and vitamin supplements.

“The developing baby depends on its mom’s vitamin D levels,” Patrick said. “The baby needs the mom to have high-enough levels. Serotonin plays a very important role in shaping the brain’s structure in those early early stages.”

To further validate their theories, the researchers cited a study involving Somali mothers, who naturally absorb less sunlight due to their dark skin pigmentation. When they moved north to Stockholm, a less-sunny region, they were found to be 4.5 times more likely to have autistic children, compared to the the country’s lighter-skinned natives.

While some scientists such as Cannell call the findings “groundbreaking” and “earth-shattering,” others seem to feel little more than tremors.

“This is a theoretical paper,” said Robert Hendren, the director of UCSF’s autism and neurodevelopment program. “It is an interesting link, but there’s no cause and effect.”

Hendren argued scientists must conduct clinical trials testing the effect of vitamin D supplements on autistic patients in order to prove the theory. Hendren himself is currently in the middle of a trial but says his team has not yet run a large enough sample or come to a definitive conclusion.

But Hendren is still optimistic and unreservedly recommends vitamin D supplements to his autistic patients, some of whom have reported improvements in behavior.

“It’s a very simple solution,” Patrick said. “It’s something that can be easily done and implemented and may make a huge difference.”