(Ivanhoe Newswire) -- Using newer, more accurate measuring tools,
researchers have discovered a link between sleep apnea and pre-diabetic changes
in insulin production and glucose metabolism.
In previous studies, researchers used body mass index to measure body fat, but
scientists now believe that method is prone to errors. For this study, Naresh
Punjabi, M.D., Ph.D., and colleagues used dual-energy X-ray absorptiometry (DEXA),
a highly precise technique for assessing body fat, and frequently sampled
intravenous glucose tolerance test (FSIVGTT), which provides a detailed picture
of the person's insulin sensitivity over time rather than a simple snapshot at a
specific moment.
Scientists recruited 118 patients, including 39 who had no sleep disordered
breathing (SDB) and 79 who were newly diagnosed with SDB but who had not been
treated. Each person underwent a sleep study to assess their level of SDB, then
underwent a FSIVGGT to determine their glucose metabolism and insulin
sensitivity/production the following day.
"Our major finding was that, as we suspected, SDB was strongly associated with a
decrease in the three major metabolic pathways that the body uses to metabolize
glucose -- insulin sensitivity, glucose effectiveness and pancreatic cell
function -- independent of adiposity [obesity]," Punjabi said.
He
said this research shows that SDB is characterized by multiple physiological
deficits that increase the predisposition for type 2 diabetes.
In a separate study, researchers at Johns Hopkins Bayview Medical Center
Bariatric Surgery Clinic found that the chronic intermittent hypoxia -- a lack
of adequate oxygen supply -- that often characterizes obstructive sleep apnea (OSA)
is also independently linked to the progression of liver disease.
Researchers recruited 90 severely obese patients who were preparing to undergo
gastric bypass surgery but did not have known diagnoses of OSA, a common form of
SDB. Each person underwent a sleep study and blood tests for markers of liver
function, insulin resistance and systemic inflammation.
A link was found between OSA and insulin resistance and further linked it to the
level of hypoxemia experienced during the night versus simply the number of
apneic events.
Researchers said their findings were clear: obesity and obstructive sleep apnea
exert separate and perhaps additive negative effects on insulin resistance and
the liver.
In a separate study, Canadian researchers found yet another risk factor common
to obesity and OSA: prolonged daytime sitting or standing. In fact, even when a
sedentary lifestyle does not lead to obesity, it may still lead to OSA and its
health risks.
This is caused by a daytime fluid build-up in the calves, caused by prolonged
inactivity, shifting to the upper body at night when a person lies in bed.
"It is therefore plausible that some of the displaced fluid might reach the neck
and predispose to upper airway constriction," researchers said.
SOURCE: American Journal of Respiratory and Critical Care Medicine, February
2009
