Energy hormone: Thyroxine

Energy hormone: Thyroxine

Your thyroid gland controls your metabolism,
which is your body’s mechanism for
turning calories into energy. It’s yet another
chain of command: Your hypothalamus
detects fatigue and then your pituitary gland
signals your thyroid to secrete thyroxine.
This hormone enters almost every cell in
your body. “It boosts sugar burning and oxygen
intake in cells,” says McLachlan. “This
raises your body temperature and increases
your heart rate.”
Are your hormones in tune? When this system
is out of whack, the result can be muscle
breakdown, weakness, fatigue, and weight
gain. While most thyroxine disruptions are
genetic, there is growing evidence that some
environmental compounds can block thyroxine,
says McLachlan. A 2009 study suggests
that BPA can displace thyroxin from its
receptor and block it. Brominated fl ame
retardants (BFRs) and polychlorinated
biphenyls (PCBs) also both interfere with
your thyroid. (BFRs are found in clothes, furniture,
and electronics; PCBs, which are no
longer in use in the United States, can still be
found in the environment, particularly in
farmed salmon.) “If you’re exposed to these,
you could end up with a form of hypothyroidism—
an underproduction of thyroxine that
causes low energy and weight gain,” says
McLachlan. On the other end of the spectrum,
hyperthyroidism, or overproduction of
thyroxine, can cause anxiety, increased heart
rate, weight loss, an enlarged thyroid, and
swelling behind the eyes. Your doctor will be
able to identify thyroid problems by prescribing
a thyroid-stimulating hormone
(TSH) blood test; fi xes for both may include
surgery or dietary changes, as well as lifelong
daily doses of prescription drugs.