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Thyroid
hormones and hair growth
Little is known about the mode of action for thyroid hormones on
hair follicles, but it is clear that hair follicles are very sensitive
to thyroid hormone levels. In research studies it has been shown
that hair follicles express thyroid hormone receptors and they can
respond with increased hair growth when exposed to the thyroid derived
hormone triiodothyronine (T3).
Over a third of people with hypothyroidism (a reduced thyroid gland
activity) experience diffuse hair loss - a kind of telogen effluvium.
To some extent, thyroid hormone replacement treatment can help promote
hair growth, but many find that even with treatment the hair growth
does not fully recover. Anecdotally, there is evidence that some
thyroid hormone treatments are more effective than others in promoting
hair regrowth. In general it is suggested that the natural, animal
derived, thyroid supplements are superior for hair growth compared
to the synthetic manufactured hormone pills. However, this has not
been proven in any scientific study.
To a lesser extent people with hyperthyroidism (an overly active
thyroid gland) can also experience diffuse hair loss. So there seems
to be a a normal range of thyroid hormones that hair follicles are
happy with, but above or below this normal range hair follicles
are likely to respond by shutting down and entering a telogen resting
state.
However, occasionally there are reports of people with hypothyroidism
or hyperthyroidism experiencing hypertrichosis - an excess of hair
growth. This might be expected in people with mild hyperthyroidism,
where a modest increase in thyroid hormones may stimulate the hair
follicles into increased growth but not be so high as to be toxic
for the cells. But why some people with a lack of thyroid hormone
production should also experience hypertrichosis is not clear.
What
thyroid hormones are tested and what does it mean ?
A full blood screen should include several tests on thyroid gland
derived hormones. How test results are given differs from laboratory
to laboratory, but you should be able to relate the list below to
at least some of the figures on your test results sheet.
Thyroxine (T4). Thyroxine is measured in several different
ways. The most common test that is done in almost every thyroid
hormone screen is called "T4". The T4 test measures all
the thyroxine in blood serum - free hormone and hormone that is
bound to other proteins. The amount of free hormone is a very small
proportion of the total T4 count, usually not more than 0.05%. The
level of thyroxine can change depending on several factors including
the levels of thyroid binding globulin (TBG) and albumin protein
in the serum. A drop in thyroxine levels may be associated with,
a thyroid gland disease, a disruption of the pituitary gland (the
pituitary gland stimulates the thyroid to produce T4), high androgen
levels, liver disease and other illnesses while high estrogen levels
might increase thyroxine levels.
You might also see a value in your test results called "free
T4" or "FT4". This is the measure of the biologically
active free, unbound thyroxine in your blood. This value is pretty
stable for everyone regardless of other hormone levels and whether
you are male or female.
Triiodothyronine (T3). Another common test will normally
be listed on your results as "total T3" or just "T3".
This is a measure of the concentration of thyroid hormone triiodothyronine
in the serum - both free and protein bound. The biologically active
free triiodothyronine only accounts for about 0.5% of the total
value for T3. The value for T3 can go up or down. In hyperthyroidism
the level goes up while chronic illness can depress T3 levels. In
hypothyroidism the hormone level stays pretty much the same.
Resin T3 Uptake. You might also see a value listed as "Resin
T3 Uptake". The Resin T3 Uptake is used to assess the binding
capacity of the serum for thyroid hormone. This value determines
whether the total T4 accurately reflects the free T4 or whether
abnormalities in binding capacity are responsible for changes in
T4 values. In this test a labeled hormone is added to the serum
to be tested. If there is an increase in binding capacity more of
the added, labeled hormone will be bound to the binding proteins
and thus less will be left free in the serum. The remaining free
labeled hormone is measured and reported as a percentage of the
total labeled hormone that was added. If the resin T3 uptake value
is normal or elevated and total T4 or T3 is high then it indicates
a direct excess production of thyroid hormones (hyperthyroidism).
If the resin T3 uptake value is low but the total T4 or T3 is high
it suggests there is a high thyroid binding protein level. If the
binding capacity is increased because of high estrogens, the free
labeled hormone will be decreased and the Resin T3 uptake will be
decreased. The T4 Uptake is a similar test.
Reverse T3. The Reverse T3 (RT3) value can help to define
between hypothyroidism and the changes in thyroid function associated
with acute illness. RT3 has little or no biological activity and
is simply a metabolite and method of disposal for T4. During periods
of starvation or severe physical stress, the level of RT3 while
increase while the level of T3 decreases. In hypothyroidism both
RT3 and T3 levels decrease.
Thyroid stimulating hormone (sTSH or TSH). In normal individuals,
thyroid stimulating hormone (sTSH or TSH) is usually between 0.5
and 5.0 mU/ml. TSH levels are modulated by a negative feed back
loop controlled by the amount of free thyroid hormone (T4 and T3).
So high free T4 and T3 should mean low TSH. The level of hypothalamic
thyroid releasing hormone (TRH) positively influences TSH. More
TRH means more TSH.
In thyroid hormone deficiency due to failure of the thyroid gland
the TSH level is usually elevated due to low T4 and T3. If hypothyroidism
develops due to failure of the pituitary gland, that produces TSH,
or the hypothalamus, that produces TRH, the values for TSH may be
low, normal or occasionally in the borderline range. A TSH value
greater than 20 mU/ml is a good indicator of primary failure of
the thyroid gland. A value of between 5 and 15 is a borderline value
which may require more careful evaluation. A TSH value below 5 is
good evidence against primary hypothyroidism. The presence of low
Free T4 with a TSH of less than 10 strongly suggests a pituitary
or hypothalamic etiology for the hypothyroidism (secondary hypothyroidism).
High levels of free thyroid hormone suppress TSH levels. So in
most cases of hyperthyroidism the TSH values will be less than 0.3
and usually less the 0.1 mU/L. Where TSH levels are suppressed in
patients a measurement of free T4 and T3 is also required to define
the degree of hyperthyroidism. TSH levels, along with free T4 and
T3 levels, can also be effectively used to follow patients being
treated with thyroid hormone. High TSH levels usually indicates
under-treatment, while low values usually indicate over-treatment.
Antithyroid Antibodies. Thyroid diseases can involve the
production of antibodies that target various proteins in the thyroid
gland. These antibodies can play a fundamental role in the development
of disease. Three main classes of antibodies are looked for, Antithyroid
Microsomal Antibodies, Antithyroglobulin, and Thyroid Simulating
Immunoglobulin. People with a subclinical state or full blown autoimmune
thyroiditis (Hashimoto’s thyroiditis) usually have high levels
of Antithyroid Microsomal Antibodies. Antithyroglobulin antibodies
may also be elevated in patients with autoimmune thyroiditis. Thyroid
Stimulating Immunoglobulins are associated with Grave’s Disease
and are the likely cause of the hyperthyroidism seen in this condition.
These antibodies attach to the thyrotropin (TSH) receptor in the
thyroid gland and activate it making the cells produce more hormones
than they normally would.
Standard
ranges of thyroid hormones
Note; only the basic adult ranges are listed here. During pregnancy,
normal thyroid activity undergoes significant changes that are not
listed below. The values for children are also significantly different.
Normal ranges will be slightly different in different laboratories
as there is no calibration of the tests between different labs.
| Hormone test |
Adult male |
Adult female |
| Serum resin thyroxine uptake (standard units or
standard international units) |
25-35% Standard units or 0.2-0.35
SI units |
25-35% Standard units or 0.2-0.35
SI units |
| Total serum thyroxine (T4) (micrograms per deciliter
or nano-moles per liter) |
5.0-12.0 µg/dL or 64.4-154.4
nmol/L |
5.0-12.0 µg/dL or 64.4-154.4 nmol/L
|
| Free serum thyroxine (free T4) (nanograms per
deciliter or pico-moles per liter) |
0.9-2.0 ng/dL or 12-26 pmol/L |
0.9-2.0 ng/dL or 12-26 pmol/L
|
| Total serum triiodothyronine (T3) (nanograms per
deciliter or nano-moles per liter) |
95-200 ng/dL or 1.5-3.0 nmol/L |
95-200 ng/dL or 1.5-3.0 nmol/L
|
| Free serum triiodothyronine (free T3) (nanograms
per deciliter or pico-moles per liter) |
0.2-0.52 ng/dL or 3-8 pmol/L |
0.2-0.52 ng/dL or 3-8 pmol/L
|
| Serum reverse triiodothyronine (nanograms per
deciliter or nano-moles per liter) |
25-75 ng/dL or 0.39-1.5 nmol/L |
25-75 ng/dL or 0.39-1.5 nmol/L |
| Thyroid-stimulating hormone (TSH) (microunits
per milliliter) |
0.5 –5.0 µU/ml |
0.5 –5.0 µU/ml |
| Serum thyroglobulin (nanograms per milliliter
or micrograms per liter) |
Less than 40 ng/mL or less than
40 µg/L |
Less than 40 ng/mL or less than
40 µg/L |
| Serum thyroxine to thyroglobulin ratio (standard
units or standard international units) |
2.7-6.4 Standard units or 0.2-0.5
SI units |
2.7-6.4 Standard units or 0.2-0.5
SI units |
| Serum free thyroid hormone indices unadjusted
(standard units or standard international units) |
1.3-4.2 Standard units or 16-54
SI units |
1.3-4.2 Standard units or 16-54
SI units |
| Serum free thyroid hormone indices adjusted for
thyroid binding globulin (standard units or standard international
units) |
5-12 Standard units or 64-154 SI
units |
5-12 Standard units or 64-154 SI
units |
Standard
ranges of thyroid hormones references
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