A double whammy of darkness and the availability of high-sugar food can make Christmas depressing for many, according to scientists.

A 'perfect storm' of winter blues and gorging on sugary seasonal sweets - causing a drop in mood - are the culprits, according to a new study.

Christmas baking table scene with assorted sweets and cookies, top view over a rustic wood background

Dr. Stephen Ilardi explained, "When we consume sweets, they act like a drug. They have an immediate mood-elevating effect, but in high doses, they can also have a paradoxical, pernicious longer-term consequence of making mood worse..." (iStock)

Researchers believe it is a vicious cycle, prompting them to warn against those feeling low to reach for the box of chocolates or mince pies for a temporary boost.

In fact, eating too many sweets can be as physically and psychologically damaging as drinking too much alcohol, say the researchers.

According to the scientists, winter-onset depression is brought on by a lack of sunlight at this time of year, which plays havoc with human beings' natural wake/sleep cycle.

This sleep disruption is responsible for pushing one in 10 people into a full-blown episode of clinical depression but the condition affects around a third.

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Dr. Stephen Ilardi, associate professor of Clinical Psychology at the University of Kansas, USA, explained: "One common characteristic of winter-onset depression is craving sugar. So, we've got up to 30 percent of the population suffering from at least some symptoms of winter-onset depression, causing them to crave carbs - and now they're constantly confronted with holiday sweets."

Dr. Ilardi continued: "When we consume sweets, they act like a drug. They have an immediate mood-elevating effect, but in high doses, they can also have a paradoxical, pernicious longer-term consequence of making mood worse, reducing well-being, elevating inflammation and causing weight gain. Alcohol is basically pure calories, pure energy, non-nutritive and super-toxic at high doses. Sugars are very similar. We're learning when it comes to depression, people who optimize their diet should provide all the nutrients the brain needs and mostly avoid these potential toxins."

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He added: "A large subset of people with depression have high levels of systemic inflammation. When we think about inflammatory disease we think about things like diabetes and rheumatoid arthritis - diseases with a high level of systemic inflammation. We don't normally think about depression being in that category, but it turns out that it really is - not for everyone who's depressed, but for about half. We also know that inflammatory hormones can directly push the brain into a state of severe depression. So, an inflamed brain is typically a depressed brain. And added sugars have a pro-inflammatory effect on the body and brain."

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The conclusions, published in the journal Medical Hypotheses, is based on a wide range of research on the effects of consuming added sugar.

In the study, the researchers found microbes in the body able to "hack" the brain - causing inflammation and low mood - fed off sugars.

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Dr Ilardi said: "Many of those parasitic microbes thrive on added sugars, and they can produce chemicals that push the brain in a state of anxiety and stress and depression.