HOW CORTISOL LEVELS AFFECT THYROID FUNCTION AND AGING
Interview with David Zava, Ph.D
JLML: Cortisol is needed for nearly all dynamic processes in the body, from blood pressure regulation and kidney function, to glucose levels and fat building, muscle building, protein synthesis and immune function. You’ve been specifically studying the effects of cortisol on thyroid function.
DTZ: Yes, one of cortisol’s more important functions is to act in concert or synergy with thyroid hormone at the receptor-gene level. Cortisol makes thyroid work more efficiently. A physiologic amount of cortisol—not too high and not too low—is very important for normal thyroid function, which is why a lot of people who have an imbalance in adrenal cortisol levels usually have thyroid-like symptoms but normal thyroid hormone levels.
JLML: Would you explain this thyroid-cortisol relationship in more detail?
DTZ: One way to understand the synergy of cortisol and thyroid is to think of trying to turn on a big round valve with one hand, as opposed to two hands where you can really grip it and turn it on. Both thyroid and cortisol have to be there in the cells, bound to their respective receptors at normal levels, to efficiently turn the valve on and get gene expression. So, when cortisol levels are low, caused by adrenal exhaustion, thyroid is less efficient at doing its job of increasing energy and metabolic activity.
Every cell in the body has receptors for both cortisol and thyroid and nearly every cellular process requires optimal functioning of thyroid.
JLML: And what happens when cortisol levels get too high?
DTZ: Too much cortisol, again caused by the adrenal glands’ response to excessive stressors, causes the tissues to no longer respond to the thyroid hormone signal. It creates a condition of thyroid resistance, meaning that thyroid hormone levels can be normal, but tissues fail to respond as efficiently to the thyroid signal. This resistance to the thyroid hormone signal caused by high cortisol is not just restricted to thyroid hormone but applies to all other hormones such as insulin, progesterone, estrogens, testosterone, and even cortisol itself. When cortisol gets too high, you start getting resistance from the hormone receptors, and it requires more hormones to create the same effect. That’s why chronic stress, which elevates cortisol levels, makes you feel so rotten—none of the hormones are allowed to work at optimal levels.
Insulin resistance is a classic example. It takes more insulin to drive glucose into the cells when cortisol is high. High cortisol and high insulin, resulting in insulin resistance, are going to cause you to gain weight around the waist because your body will store fat there rather than burn it.
JLML: This would certainly be a significant effect when it comes to creating balanced hormone levels.
DTZ: When cortisol is high the brain also is less sensitive to estrogens. That’s why you can have a postmenopausal woman with reasonable amounts of estrogen, but when you put her under a stressor and her cortisol rises, she’ll get hot flashes, which are a symptom of estrogen deficiency. She really doesn’t have an estrogen deficiency, the brain sensors have just been altered. If you then drive the estrogen levels up with supplementation to treat the hot flashes, she’ll start getting symptoms of estrogen dominance like weight gain in the hips, water retention, and moodiness. And the hot flashes usually don’t go away.
This is why you often can’t effectively treat someone with hormonal imbalance symptoms such as hot flashes by simply adding what seems to be the missing hormone, be it thyroid, progesterone, estrogen or testosterone. If your cortisol is chronically high you’ll have overall resistance to your hormones.
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