Thanks for your question. That's a good one because, as you imply, many midlife women do develop underactive thyroid glands. Given that some of the common experiences in perimenopause resemble too little thyroid hormone (hypothyroidism), it is important for women to be able to sort out for themselves where the problem lies.
I'd like to answer your question by first describing what perimenopause and hypothyroidism have in common. Then I'll discuss the most reliable experiences that tell you your thyroid gland is not making enough thyroid hormone. And finally I'll describe how to sort out the experiences of perimenopause from those of an under active thyroid gland.
What perimenopause and hypothyroidism have in common:
Both occur commonly in midlife women. Thus, perimenopause happens for all women and hypothyroidism increases with increasing age especially in women, therefore, perimenopause and new onset hypothyroidism may occur together.
Perimenopause is universal - every woman "gets" it. Perimenopause is the normal transition between potentially fertile menstrual cycles and menopause, the final phase of reproductive life that begins a year after the last period. Perimenopause can start between the mid-30s and the late 40s. Menopause occurs at an average age of 51 but can begin normally between ages 40 and 58.
Underactive thyroid hormone, although it is common, occurs for something like 30-40% of women, and thus is not at all inevitable. It is more frequently a problem for women than men and is diagnosed more and more with increasing age in both. Although there are many reasons for an underactive thyroid, the most common one is that the gland becomes unable to make enough thyroid hormone, usually because the body attacks the thyroid tissue as though it were foreign (often called Hashimoto's thyroiditis). Instead of having a good production of thyroid hormone, the thyroid hormone making part of the gland gets packed with lymphocytes, cells responding to the perceived "immune threat." As the thyroid hormone levels start to decrease, the brain and pituitary sense this and thyroid-stimulating hormone (TSH) is made in increasing amounts. Therefore the thyroid gland tries to make more hormone - but, because production is inefficient, the gland makes a jelly substance called colloid, many cysts and the gland gets bigger. (Hypothyroidism can also be caused by not enough of the essential mineral, iodine. For that reason, iodine is put into table salt and the problem is now rare.)
Both hypothyroidism and perimenopause are associated with weight gain. The thyroid gland controls fuel-efficiency and keeps our metabolism in kilter. With too little thyroid, the fuel (our food) is burned at a lower rate and, if eating is the same, weight gain occurs. Only in severe hypothyroidism is the body's temperature lower than normal. Although weight gain often occurs with hypothyroidism, it is a nonspecific change because increasing weight also occurs with decreased exercise (for a million reasons), with snacking to cope with stress, and as a side effect of many drugs. Typically, however, there is a significant 10-year 5-10 kg average weight gain for healthy perimenopausal women whose thyroid hormone levels are normal. This weight gain appears to be related to the two main hormonal changes of perimenopause - estrogen levels that are higher than normal and progesterone levels that are too low.
Higher estrogen causes weight gain through "insulin resistance" and by stimulation of increased body fat. Insulin is a hormone from the pancreas whose job is to let sugar get into cells where it is "burned." Insulin resistance, a problem we can detect through an increased waist size of more than 88 cm (35 inches) as fat accumulates around our internal organs, means that the insulin levels rise because the higher fat is less sensitive than muscle. Insulin levels need to be higher to do the same amount of work. That higher insulin, in turn, causes increased appetite. Higher estrogen levels typical of perimenopause also make us lay down fat, especially abdominal and subcutaneous fat.
The second reason for weight gain in perimenopause is that progesterone levels are too low. Progesterone, responsible for raising the basal temperature during the second half of the ovulatory menstrual cycle, makes us burn about 300 extra calories a day. Without progesterone, we don't burn and instead store the extra energy.
How can I tell hypothyroidism and perimenopause apart?
The most reliable symptom of an underactive thyroid gland is a relentless coldness in the centre of the body. A patient of mine, an older man with hypothyroidism, dressed in long underwear and two shirts in the summer, once growled in the characteristically low and croaky voice of those with a very low thyroid levels, "Doc, yah got to get the heat back in me!" What's interesting is that cold hands and feet, especially indoors or in a warm environment, are not a reliable sign of hypothyroidism. Rather, the "frozen fingers" are more typical of the high-estrogen amplified stress of perimenopause. They are caused by high levels of catecholamines (like epinephrine), stress hormones made in the centre of the adrenal gland that make the finger blood vessels constrict and hence the hands cool.
Perimenopause may also have issues of temperature control. Often perimenopausal "thermostat troubles" begin with night sweats initially occurring intermittently and around flow, and later during both day and night hot flushes. Following a hot flush, a perimenopausal (or menopausal) woman may become chilled as the sweat evaporates. This might make her consider her thyroid underactive. However, she should recognize the difference because: the coldness is intermittent, and it is not preceded by a wave of heat and sweating. Sometimes women who chill easily with hot flushes call them "cold sweats."
If weight gain is occurring in a midlife woman who doesn't have a chronic central coldness, it is likely perimenopausal. In either case, increasing exercise, avoiding sweets and eating sensibly will help control it.
Both hypothyroidism and perimenopause may cause sleep problems. The typical kind of sleep disturbance for a perimenopausal woman is mid-sleep wakening. She often will fall asleep instantly and sleep soundly for a few hours only to jolt awake in the wee hours of the morning. Then it is difficult to get back to sleep. The sleep problems for a woman with hypothyroidism are usually that eight, nine or 10 hours are not enough and she wakes feeling still tired.
Both hypothyroidism and perimenopause may cause low energy and fatigue. For the hypothyroid woman it may be that she just feels tired plus needs more sleep than is reasonable for any person to get. For the perimenopausal woman, she is usually tired because she's been awake in the night, with or without night sweats.
Hypothyroidism and perimenopause cause periods changes and heavy bleeding. The usual woman with either, however, has regular periods. It is much more typical, in my experience, for heavy flow to occur with regular cycles in perimenopause than in hypothyroidism. Hypothyroidism is rarely a cause of abnormal menstrual cycles but they may come every two weeks and be heavy. Unfortunately many thyroid experts describe period problems as though they were common for hypothyroidism.
Both hypothyroidism and perimenopause may be associated with depression. One of the first things that a family doctor thinks when a woman comes in complaining of low energy and needing more sleep, or sleep problems, is that she is depressed. Although both perimenopause and hypothyroidism may occur in women who are also depressed, the hormonal and social changes of each may make depression more common. The key depression question is: do you feel sad, and less interested in things that would normally make you happy?
How can I tell if it is perimenopause or hypothyroidism?
If you are feeling cold in your middle and tired despite eight hours of sleep, and gaining weight without eating differently, watch the V in your neck as you swallow. If you see a swelling there, you may have an enlarged thyroid gland. However, if you are intermittently hot and only cold after a hot flush, you are gaining weight, especially in the middle, you wake at night and are having night sweats, you are likely in perimenopause.
There is no blood test that makes a diagnosis of perimenopause - take a look at the CeMCOR website for more information. There is, however, a blood test that is a good indicator of hypothyroidism - the TSH test. The TSH level should be higher than normal or at least in the top quarter of the normal range. If the TSH is sort of high, and everything points to hypothyroidism, then it is useful for your doctor to order the Free T4 test to confirm low thyroid. The Free T4 should be in the low part of the normal range or absolutely low. If the test results are both changed in the directions to make you suspicious, but still normal, ask for a repeat TSH test in six months. Although it is a relief to find out something diagnosable, and that can explain your symptom is wrong, it is not good to take thyroid hormone therapy when you don't need it. Especially high levels of thyroid (enough to make your TSH too low) will cause increased bone loss and be demanding and dangerous for your heart.
I hope this is helpful for you,
All the best,
Jerilynn
