®® The findings identify melatonin as a
“fascinating new target” for diabetes treatments, says endocrinologist Leif Groop
of Lund University in Malmö, Sweden, a
coauthor on two of the new reports.
Two studies, one listing 108 coauthors,
pooled data from earlier studies that had
measured blood sugar levels and had collected DNA samples from participants.
The larger study included 36,610 people;
the other had 2,151. All participants were
of European descent.
In both studies, people with a single
DNA change in the gene MTNR1B , which
encodes the receptor protein that senses
melatonin, were more likely to have high
blood sugar levels and develop diabetes
than those without the DNA change.
“The finding that the melatonin receptor has an influence on diabetes was
unexpected,” Groop says.
A third paper analyzed data on over
18,000 participants from two earlier studies. It showed that the same DNA change
in MTNR1B — a seemingly innocuous G
instead of the more common C — was
linked to high blood sugar levels, low insulin levels and most important, a greater
risk of developing type 2 diabetes.
The researchers also looked at how
melatonin might directly interact with
The melatonin receptor had been says the identification of the melatonin
thought to reside primarily in the receptor as an important regulator of
brain — home of the body’s master clock. blood sugar fits well with earlier studies
Groop and his colleagues showed that looking at the effects of poor sleep on
insulin-producing beta cells blood sugar levels.
in the pancreas of mice, rats In 2007, Gangwisch showed
and humans also have the that people who get less than
melatonin receptor. five hours of sleep a night are
Its presence on the insu- significantly more likely to
lin-secreting cells suggests have type 2 diabetes. Other
that the melatonin receptor lab experiments confirm this
an influence on
may directly control insulin trend: Healthy young adults
production. When scientists prevented from entering deep
added melatonin to human sleep for just three nights
beta cells in the lab, insulin couldn’t properly regulate
production went down. A connection blood sugar levels, at least temporarily,
between melatonin and insulin makes a 2008 study showed. What’s more, the
sense since in the dead of night, when subjectsbecamemoreresistant to insulin
melatonin levels are high, the need for during the study, eventually reaching lev-insulin should be low. Researchers don’t els of insulin sensitivity that resemble the
yet know how melatonin levels are dif- insulin resistance of diabetic people.
ferent in sleep-deprived people, nor Sleep-deprived subjects, Gangwisch
how this difference could lead to higher says, crave starchy, sweet foods and don’t
blood sugar levels. regulate blood sugar well.
Thelinkbetweensleepandbloodsugar “This paper ties those two things
didn’t surprise some sleep research- together,” says Gonçalo Abecasis of
ers. Buxton says that evidence for that the University of Michigan School of
relationship has accumulated for years. Public Health in Ann Arbor, and a co-
“However, such a direct role for mela- author of one of the studies. “Sleep dis-tonin was very surprising,” he says rupts the circadian clock, and the mela-
Researcher James Gangwisch of tonin receptor disrupts the circadian
Columbia University in New York City clock. These are two different ways to
interrupt the clock, but both lead to the
same endpoint of diabetes.”
Buxton says these findings raise “more
exciting questions than they answer.” He
cautions that the work on melatonin’s
impact on insulin-producing cells in
humans is still preliminary. Many more
studies are needed before scientists will
fully understand how melatonin affects
blood sugar levels and type 2 diabetes.
Groop agrees, pointing to the need for
additional basic studies on the melatonin
receptor and clinical tests of blood sugar
levels in people who have been given
People taking melatonin to aid sleep
may be just such a group. “It would be
interesting to track incidences of diabetes in such people,” says Abecasis. s
From 1985 to 2006, the percentage of U.S. adults reporting six hours of sleep or less rose for all
age groups. Researchers asked 169,127 participants in 1985 and 23,679 i n 2006 about their
sleep habits. Over 30 percent of adults age 30 to 64 said they got too little shut-eye in 2006.
People reporting less than 6 hours of sleep per 24-hour period
18–29 30–44 45–64 65–74 > 7 5
Percent of respondents