A listener wrote to ask about some surprising dietary advice she came across in Dan Beutner’s Blue Zones Kitchen.
People with low thyroid function appear to live longer. So why are drugs to boost thyroid levels among the most commonly prescribed medications?
Nutrition Diva is hosted by Monica Reinagel. A transcript is available at Simplecast.
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Hello. I’m Monica Reinagel and you’re listening to the Nutrition Diva podcast, a show where I take a closer look at nutrition trends and headlines, explain what the latest research means for you, and answer your nutrition questions. Welcome!
Today’s episode is a continuation of a conversation prompted by Nutrition Diva listener Sandy.
She wrote to ask about some surprising dietary advice she came across in Dan Beutner’s Blue Zones Kitchen.
The Blue Zones project is an attempt to codify the dietary and lifestyle habits of the planet’s longest-living populations, with the hopes that we might learn how to live longer ourselves. My previous episode (#714) includes a bit more background on the Blue Zones, as well as an exploration of the idea that diets with less variety might actually be healthier. If you missed that, you might want to check that out.
Today, I want to dig into the claims that eating cruciferous vegetables can help you live longer by suppressing thyroid function. Gianni Pes, one of the researchers involved in the Blue Zones project explains it this way: “A low-functioning thyroid may help you live longer, in the way that a Cricket lighter with the flame turned down lasts longer.’”
Sandy wrote, “I take prescription medication daily to increase my thyroid function. If a slower metabolism is preferable for life expectancy, I have to question why my doctor would encourage me to speed mine up?”
Sandy is certainly not the only one in this situation. Low thyroid function (or hypothyroidism) is thought to affect about 1 in 20 individuals—but most of them remain undiagnosed and untreated. Even so, thyroid replacement hormone is one of the most commonly prescribed medications, with physicians writing 100 million prescriptions a year for it.
Hypothyroidism is more common in women and in people over 60. It’s usually diagnosed by a routine blood test, which your doctor might order if you report things like feeling cold all the time, unexplained weight gain, fatigue, or dry skin. Depression can also be a symptom of low thyroid function, so before treating depression with anti-depressant drugs, it’s worth checking to see if low thyroid function might be an issue.
Having low thyroid function can cause you to feel unwell, and treatment with thyroid replacement can make you feel a lot better. But it’s not just about symptom management. Over time, low thyroid function can lead to high blood pressure, high cholesterol, reduced blood flow to the organs, and an increased risk of heart failure. So, it’s not harmless.
Despite all of this, some research suggests that low thyroid function is associated with increased longevity. And this appears to have led Dr. Pes to hypothesize that a diet that suppresses thyroid function might prolong life.
The thyroid does regulate metabolism and Pes is not the first to suggest that a slightly less active metabolism might prolong life, sort of the way that always driving your car at slower speeds might prolong the life of the engine (as well as increase your gas mileage). This is one of the mechanisms by which intense calorie restriction is thought to extend life span.
For those who may not be familiar, calorie restriction (or CR) when practiced for life extension is not about losing weight (although that is an inevitable side effect). It’s about deliberately maintaining a very low body weight for the express purpose of extending life—based mostly on experiments showing that mice and fruit flies live longer when you underfeed them.
You can probably see all of the potential issues with this, but I’ll quickly list a few:
Similarly, one might wonder whether a longer life would be worth living with the symptoms and side effects of low thyroid function.
Fortunately, I don’t think we need to choose. I want to respectfully push back on Dr. Pes’ hypothesis from a couple of directions.
First, let’s take a look at the association between low thyroid function and lifespan.
The studies that have noted this association were specifically looking at centenarians, people who had lived to an exceptionally old age, to see what they had in common. One of the things they seemed to have in common was higher TSH levels, a hormone that rises as thyroid function falls.
This gets a little tricky so let me repeat that. Low thyroid function is associated with higher TSH levels, and lower TSH levels are associated with higher thyroid function.
As we know, association does not imply causation. Thyroid function naturally declines with age, so it makes sense that TSH levels would be higher in people who have managed to live longer. That doesn’t necessarily mean that this is the reason they lived longer.
The association between thyroid function and longevity was also observed in very homogenous populations—meaning, ones with a relatively tight gene pool. It’s certainly possible (even probable) that a lot of people in this population carried genes that promoted exceptional longevity as well as genes that promoted low thyroid function. But, again, correlation is not causation.
And, finally, it’s important to note that the levels associated with longer longevity suggested thyroid function at the low end of the normal range, and not clinically hypothyroid. For me, the take home would be that low thyroid function should be treated, but not over-corrected. Aiming for the low-normal end of the range, rather than the high-normal end, might be a more appropriate way to hedge your bets, rather than embracing hypothyroidism as an anti-aging strategy.
Now, let’s talk about whether cruciferous vegetables actually suppress thyroid function. This is a question I often get from the perspective of being afraid that eating Brussels sprouts will reduce thyroid function, as opposed to eating Brussels sprouts in order to suppress thyroid function. But the answer is the same either way,.
Cruciferous vegetables, which also include cabbage, kale, and broccoli, contain a natural compound that, in large amounts, can interfere with your body’s ability to metabolize the mineral iodine.
Your body needs iodine in order to make thyroid hormone and if iodine is lacking—either because your diet is deficient in the nutrient or because something is inhibiting its uptake—your thyroid hormone levels can sink. When this happens, your thyroid gland can become enlarged. That’s your body’s way of trying to increase thyroid hormone production. An enlarged thyroid, which looks like a swelling in the neck, is known as a goiter.
The good news is that goiters caused by iodine deficiency can be easily reversed: once iodine is added to the diet, the thyroid can produce enough thyroid hormone and the gland shrinks back to its normal size.
Goiters used to be much more common than they are today—and not because people ate more broccoli back then! Most goiters are caused by diets that are too low in iodine. Fortunately, since the advent of iodized salt, iodine deficiency is pretty rare these days.
Hypothyroid disease, especially the kind that runs in families, is not caused by iodine deficiency. It’s usually caused by an auto-immune condition where the body attacks and slowly destroys the thyroid gland. Once that happens, no amount of iodine is going to fix it. Instead, people with this type of thyroid disease take thyroid replacement hormone.
Even if you have thyroid disease in the family, eating goitrogenic vegetables does not increase your risk of getting it. And being treated for thyroid disease does not mean that these otherwise nutritious vegetables need to be off the menu. Assuming that your diet contains a sufficient amount of iodine, you can eat these foods on a daily basis without worrying about interfering with your thyroid function.
I looked for and could not find data on iodine deficiency or thyroid function in the Sardinian population that Dr. Pes studies. For that matter, it’s not clear that consumption of cruciferous vegetables was notably high. I could be wrong here but, to the extent that cruciferous vegetables uniquely contributed to the longevity of the Sardinians, I’m guessing it had more to do with the nutrients these vegetables provide than their effects on thyroid function.
But trying to reduce the secrets of the Blue Zones to a single gland or class of vegetables is really missing the point. Obviously, the genes that set you up for longevity are not something we can bake into a soup or stew. Nor can most of us opt out of our office jobs and take up sheep-herding.
But these Blue Zone communities do have some features in common that are more exportable—and suggest best practices for healthy aging. Most of them have nothing to do with food or diet, but center around community, purpose, and balance. The dietary recommendations are simple and basically echo Michael Pollan’s timeless advice—Eat food. Not too much. Mostly plants. (You can read more about the Blue Zones in the best-selling book by that title or at bluezones.com.)
Thanks again to Sandy for prompting this exploration of the links between thyroid function, cruciferous vegetables, and longevity. I hope you found it helpful as well as interesting. If you have a question you'd like me to answer, you can email me at nutrition@quickanddirtytips.com You can also leave me a message at 443-961-6206
I’d also like to invite you to check out my other podcast. It’s called the Change Academy, where we explore the art and science of creating positive behavior change, both in our own lives and in our workplaces and communities. You can find it on all the major podcast platforms. Just search for Change Academy.