Research out of the University of Kansas that was published in Medical Hypotheses and summarized in Neuroscience News indicates that consumption of excess sugar leads to an inflammatory response in the body and neurobiological responses that can result to depressive symptoms.  Lack of exposure to sunlight during winter months triggers the body to crave sweets, especially in the 5-10 percent of the population who are susceptible to seasonal depression. Those sweets can have a temporary lifting effect, but can also trigger symptoms.

The study authors suggest that although there is no one-size-fits-all quantity, it may be best to limit added, processed sugars to 25g per day.

For more information, the Neuroscience News article may be read here, and the study itself may be accessed here.