Higher rates of refined sugar consumption have been associated with higher rates of depression. Photo courtesy of Pixabay
July 28 (UPI) -- The thought of a
cupcake, skillfully frosted with fluffy vanilla icing, may put a smile
on your face, but research suggests that, in the long term, a sweet
tooth may turn that smile into a frown - but not for the reasons you
think. In a
new study, published in Scientific Reports, my colleagues and I found a link between a diet high in sugar and common mental disorders.
The World Health Organization
recommends
that people reduce their daily intake of added sugars (that is, all
sugar, excluding the sugar that is naturally found in fruit, vegetables
and milk) to less than 5 percent of their total energy intake. However,
people in the U.K. consume
double - in the United States
triple
- that amount of sugar. Three-quarters of these added sugars come from
sweet food and beverages, such as cakes and soft drinks. The rest come
from other processed foods, such as ketchup.
At the same time, 1 in 6 people worldwide suffers from a
common mental disorder, such as a mood or anxiety disorder. Could there be a link between high sugar consumption and common mental disorders?
Earlier
research,
published in 2002, examined the link between depression and sugar
consumption in six countries. The researchers, from Baylor College,
found that higher rates of refined sugar consumption were associated
with higher rates of depression.
Since then, a handful of studies have investigated the link between added sugar consumption and subsequent depression. In 2011,
researchers in Spain
found that when they grouped participants based on their commercial
baked food consumption, those who ate the most baked food had a 38
percent increased chance of developing depression compared with those in
the group with the lowest intake. The association remained even after
accounting for health consciousness and employment status.
In 2014, researchers studied the association between sweetened beverages in
a large U.S. group.
They found that sugar-sweetened and artificially sweetened drinks (diet
drinks) could increase a person's risk of developing depression. And,
more recently,
a 2015 study,
including nearly 70,000 women, found higher chances of depression in
those with a high added sugar intake, but not in those with a high
intake of naturally occurring sugars, such as those found in fruit.
Trying to explain the link
We are still not sure what causes depression, but some researchers
believe that biological changes are at the root of it. Some of these
changes could be influenced by sugar and sweet taste. For example, a
study
in rats found that diets high in sugar and fat can reduce a protein
called BDNF that influences the growth and development of nerve cells in
the brain. This protein is thought to be involved in the development of
depression and anxiety.
Another possible biological cause is inflammation. High-sugar diets can increase
inflammation
- a protective reaction of the body, normally directed against
microorganisms or foreign substances. While common signs of
inflammation, such as redness, are far from a mood disorder, the
symptoms that keep us in bed with a cold are much closer, such as low
energy and being unable to concentrate. Ongoing
research suggests that mood disorders could be linked with inflammation, at least in some cases.
Dopamine is another possible culprit. A
study
using rats earned headlines for suggesting sweet foods could be as
addictive as cocaine. This might be due to affects on dopamine, a brain
chemical involved in the
reward system.
Dopamine is also thought to influence mood. And addiction is itself
associated with a higher risk of developing a mood disorder.
Finally, sugar intake could be associated with other factors, such as obesity, which itself is related to mood.
But these associations could also reflect a reverse phenomenon: Low
mood could make people change their diet. Sweet foods could be used to
soothe bad feelings by providing a
short-term mood boost.
And low mood and anxiety could make simple tasks, such as grocery
shopping or cooking, so difficult and exhausting for the sufferer that
they might start to avoid them. Instead, they might opt for junk food,
takeout and ready meals - all of which have a high sugar content.
What our study adds to the debate
For our latest study, my colleagues and I put the reverse association
idea to the test. We used sugar intake from sweet food and drinks to
predict new and recurrent mood disorders in a group of British civil
servants. We also investigated whether having a mood disorder would make
people more inclined to choose sweet foods and drinks.
We found that men without a mood disorder who consumed over 67g of
sugar had a 23 percent increased risk of suffering from a mood disorder
five years later, compared with those who ate less than 40g. This effect
was independent of the men's socioeconomic status, physical activity,
drinking, smoking, other eating habits, body fat and physical health.
We also found that men and women with a mood disorder and a high
intake of sugar from sweet food and drinks were at higher risk of
becoming depressed again five years later, compared with those who
consumed less sugar. But this association was partly explained by their
overall diet.
We found no evidence for a potential reverse effect: Participants did
not change their sugar intake after suffering from mood disorders.
Despite
our findings, a number of questions remain about whether sugar makes us
sad, whether it affects men more than women, and whether it is
sweetness, rather than sugar itself, that explains the observed
associations. What is certain, though, is that sugar is associated with a
number of health problems, including tooth decay, type 2 diabetes and
obesity. So cutting down on sugar is probably a good idea, regardless of
whether it causes mood disorders or not.
When News Breaks Out, We Break In. (The 2014 Bloggies Finalist)
