New York, Aug 15 (IANS): Lower levels of a brain chemical that regulates mood, sleep and appetite may be a key player in cognitive decline and not just a side-effect of Alzheimer's disease -- as previously believed, researchers have found.

Previous studies have shown that people with Alzheimer's disease and severe cognitive decline have loss of serotonin neurons.

The new study led by researchers at the Johns Hopkins University in the US, of people with very early signs of memory decline, suggests that lower serotonin transporters may be drivers of the disease than a byproduct.

Serotonin levels that are lower and out of balance with other brain chemicals such as dopamine are well known to significantly impact mood, particularly depression.

The report suggested that finding ways to prevent the loss of serotonin or introducing a substitute neurotransmitter could slow or stop the progression of Alzheimer's disease and perhaps other dementias.

"Now that we have more evidence that serotonin is a chemical that appears affected early in cognitive decline, we suspect that increasing serotonin function in the brain could prevent memory loss from getting worse and slow disease progression," said Gwenn Smith, Professor at the varsity.

For the study, to be published in the journal Neurobiology of Disease, the researchers recruited participants with mild cognitive impairment mainly in memory -- indicative of Alzheimer's disease -- who were paired with healthy matched controls.

The results showed that people with mild cognitive impairment had 37 per cent lower verbal memory scores and 18 per cent lower levels of serotonin transporter in the brain's hippocampus compared to healthy controls.