What causes hypothyroidism? Why is hypothyroidism more common in women than men? Several hours of research into these questions did not yield all the answers I was looking for, but here is some interesting information I found about possible causes for this all too common condition.
Autoimmune disease, where the body’s immune system mistakenly attacks the thyroid gland, is cited as the most common cause of hypothyroidism, a decreased production of the essential thyroid hormone. Hashimoto’s Thyroiditis, the most common type of autoimmune thyroiditis, was discussed in an earlier blog. Click here to read this article.
Surgery, removing part or all of the thyroid, (for example, to remove thyroid nodules or cancer), can leave the thyroid with reduced ability to produce hormone, depending on the amount of gland removed.
Radiation of the head, neck or upper chest to treat cancer or overactive thyroid can cause loss of part or all thyroid function.
Thyroiditis, inflammation of the thyroid gland, is usually caused by an autoimmune attack or viral infection. The inflamed thyroid can release stored thyroid hormone initially, causing temporary hyperthyroidism, followed by reduced function and hypothyroidism.
Medications, for example, lithium (to treat bipolar illness), amiodarone (for heart arrhythmias), interferon alpha and interleukin-2, can prevent the thyroid gland from being able to make hormone normally. Medications are more likely to trigger hypothyroidism in those with a genetic tendency.
Iodine deficiency or excess – The thyroid needs iodine to make thyroid hormone, but too much can worsen hypothyroidism. The recommended daily intake is 150 mcg in adults but amounts greater than this are generally well tolerated. Authorities recommend a maximum of 1,100 mcg daily but there is controversy around this, with amounts as high as 40 mg daily being used to treat iodine deficiency in some countries.
Iodine is contained in various foods, such as seafood, eggs, dairy products, sea weed/sea vegetables (kelp and dulse, for example), and it is added to regular table salt. The amount of iodine in vegetables will vary, depending on how much iodine was in the soil they where they were grown.
Because low iodine can be a cause of severe mental retardation, as well as thyroid dysfunction, the mineral is added to table salt. However, for those with salt restricted diets, of course I this is no longer a source.
Genetic factors may play a role; if close family members have developed hypothyroidism, you are likely at greater risk of developing it also.
Pregnancy – The increase in risk is thought to be due to increased antibody production during pregnancy. Often, thyroid problems during pregnancy resolve after the birth, but the mother remains at increased of developing hypothyroidism again later in life. Note that low thyroid during pregnancy can increase the risk of miscarriage and birth defects.
Some, more controversial causes have been suggested, as researchers look for explanations for increases in occurrence of thyroid diseases:
Increased exposure to chlorine and fluorine (fluoride)
Chlorine, fluorine and iodine are in the same family of elements, and are prone to react in a similar manner. Some have suggested that ingesting chlorinated/fluorinated water might prevent iodine absorption or proper function. Sounds like the idea might hold water, but I didn’t find any studies to support this theory. I expect other factors would also need to be present to see this effect.
Stress may exacerbate an underlying thyroid condition (EndocrineWeb.com; Pharmacy conference)
Stress causes an increase in release of the stress hormone, cortisol.
Cortisol interferes with thyroid hormone production.
Production of reverse-T3 thyroid (which is inactive) rather than active T3 as a genetic response to stress is theorized to occur in dependants of populations who survived famine. This mechanism would have enabled increased chance of famine survival by slowing the metabolism and reducing need for food.
Today’s stresses rarely involve a lack of food, but those with this genetic trait are thought to react to modern stress as their ancestors did to the stress of famine.
When stressed, humans are considered more vulnerable to autoimmune disease (e.g. Hashimoto’s Thyroiditis)
Treating stress may help improve thyroid function, according to EndocrineWeb.com:
Mind/body techniques (relaxation, medication, yoga)
Exercise (helps reduce the effects of cortisol)
Sleep (helps cope with stress)
X-rays – If radiation treatment damages the thyroid, can low-level radiation used in x-rays cause damage over time?
Experts say, probably not: most radiation goes where intended. The rest of the body is exposed only to “scatter radiation”. One study (Mayo Clinic.org) estimated scatter radiation to the thyroid from a standard mammogram to be equivalent to 30 minutes of natural background radiation in the environment.
Repeated dental x-rays performed before 1970, when higher levels of radiation were emitted, increased risk for thyroid cancer later in life (risk of hypothyroidism was not mentioned). X-rays are safer now but the American Dental Association still stresses the need to shield the thyroid during dental x-ray examination.
Most mammogram clinics have thyroid guards but, generally, you need to ask for this protection. Mayoclinic.org states that thyroid guards can sometimes interfere with getting good images, so discuss this option with your doctor and/or x-ray technician.
So, what are the risk factors for developing hypothyroidism?
Being a woman and over age 60
One site suggested that women’s endocrine systems were “more sensitive”. This was the best explanation I found for why women developed hypothyroidism more often than men (doesn’t really explain much!)
Any autoimmune disease (for example, rheumatoid arthritis, inflammatory bowel disease)
Having a family history of thyroid problems
Treatment with radioactive iodine or anti-thyroid medications (for overactive thyroid)
Radiation treatment to the head, neck or upper chest
Thyroid surgery with partial or complete thyroid removal (amount of function will depend on how much gland was removed)
Pregnancy or birth within the past 6 months
How do you know if your thyroid is under performing? Here are some symptoms of hypothyroidism:
Fatigue
Dry skin
Constipation
Weight gain
Decreased body temperature
Intolerance to cold
If you have these symptoms, talk to your doctor. S/he will likely order a blood test to check your thyroid function:
Thyroid hormone (levothyroxine or T4) – will be below normal
Thyroid Stimulating Hormone (TSH) – will be elevated
This is the hormone that tells your thyroid to make more hormone so it increases when thyroid is low, trying to stimulate the gland to make more.
If too much thyroid, TSH production will be low. Tests for TSH are also used to check whether you are taking the correct dose of thyroid replacement.
“Normal” TSH values vary in different countries:
USA – 0.3 to 3.0
Canada – 0.5 to 4.5 or 5
Some authorities suggest we feel best when TSH is around 1 but in many areas anything in the "normal" range is considered fine.
Since excess thyroid hormone can create risk for heart disease and osteoporosis, some doctors intentionally undertreat hypothyroidism slightly.
