Men
with low testosterone should have their hormone levels retested
after they fast overnight because eating may transiently lower
testosterone levels, a new study concludes.
“Both
the incidence of low testosterone, or hypogonadism, in men
and the annual number of testosterone prescriptions are increasing,
likely as a result of the obesity epidemic and our aging population,”
said study co-author Frances Hayes, MD, an endocrinologist
at St. Vincent’s University Hospital in Dublin, Ireland, who
did the research at Massachusetts General Hospital, Boston.
“The
decision to prescribe testosterone therapy is based on the
result of a blood sample, so obtaining an accurate measurement
of testosterone is key to making a correct diagnosis of hypogonadism.”
In
current guidelines for evaluating men with hypogonadism, The
Endocrine Society recommends measuring blood levels of testosterone—the
major male sex hormone—on two or more occasions in the morning,
when testosterone is highest.
However,
no guidelines exist on when to draw a testosterone sample
in relation to food intake, Hayes said.
Past
research shows that a high level of insulin, the hormone
primarily secreted after eating, is related to low testosterone
levels. |
Like
eating, glucose intake causes blood glucose (sugar)
levels to rise, which stimulates secretion of insulin.
|
Hayes
and her colleagues examined the impact of a standard dose
of glucose on testosterone levels in 74 men.
The
researchers administered the oral glucose tolerance test,
a screening test for diabetes that involves drinking a sugary
solution (75 grams of pure glucose) and then measuring blood
sugar levels.
Of
the 74 men, 42 had normal glucose tolerance on the test, 23
had impaired glucose tolerance (also called prediabetes) and
9 had newly diagnosed type 2 diabetes.
The
authors found that the glucose solution decreased blood
levels of testosterone by as much as 25 percent, regardless
of whether the men had diabetes, prediabetes or normal
glucose tolerance. |
Two
hours after glucose administration, the testosterone level
remained much lower than before the test in 73 of the 74 men,
a statistically significant difference, the authors reported.
Of
the 66 men who had normal testosterone levels before the test,
10 (15 percent) became hypogonadal at one or more time points
during the test.
The
results did not differ by changes in insulin levels, according
to the abstract. Other hormones that could change testosterone
measurements also did not appear to affect results.
Hayes
said more research is needed to find the factor or factors
responsible for this drop in testosterone.
Because
glucose intake, and likely food, decreases
testosterone, she said, “This research supports the notion
that men found to have low testosterone levels
should be reevaluated in the fasting state.”
|
