I’ve never been a big coffee drinker, but since many people with thyroid and autoimmune thyroid conditions consume caffeine in the form of coffee, tea, and other caffeinated beverages, I figured it would be a good idea to write an updated post on this topic. Plus, since my wife drinks coffee on a daily basis I’m sure she’ll appreciate this blog post as well! I usually recommend for my patients to initially avoid caffeine (especially coffee) while trying to restore their health, and not surprisingly, many people find this to be very challenging. While there are certain risks of consuming caffeine, numerous studies show that caffeine does have some health benefits.
Caffeine is the most widely consumed psychostimulant substance (1) . As I mentioned in the opening paragraph, I have never been a coffee drinker, although my wife loves coffee, our dog Lexi loves coffee (just kidding), and many of my patients also enjoy drinking coffee on a daily basis. I do consume caffeine in other ways, such as by drinking green tea and eating some dark chocolate. Perhaps the main reason why I have most of my patients avoid caffeine initially is because it causes an elevation of ACTH and cortisol, along with the catecholamines. And since most of my patients have adrenal problems I think it’s a good idea for many of them to refrain from consuming caffeine while trying to improve their health.
Coffee (brewed): one 8-ounce cup has approximately 107 to 150 mg of caffeine
Black tea: one 8-ounce cup has approximately 28 to 46mg of caffeine
Green tea: one 8-ounce cup has approximately 25mg of caffeine
Starbucks Grande Cafe Mocha: one 16-ounce cup has approximately 175mg of caffeine
Coca-Cola Classic: one 12-ounce bottle has approximately 34 mg
Pepsi Cola: one 12-ounce bottle has approximately 40mg of caffeine
Dark Chocolate: one ounce has approximately 12mg of caffeine.
What Does The Research Show?
What I’d like to do now is discuss some of the research studies associated with the consumption of caffeine.
Caffeine and cardiovascular health. One study involving 52 healthy adults aged 18-29 years of age examined the stress reactivity following caffeine consumption (5) . The study showed that both men and women had an increase in systolic blood pressure and cortisol levels after consuming caffeine, although the CRP levels weren’t affected. Just as a reminder, CRP is a marker of inflammation. Another study examined whether a single ingestion of caffeine improves microvascular function in healthy subjects (6) . The results showed that caffeine contained in a cup of coffee enhances microvascular function in healthy individuals. A couple of meta-analyses showed an inverse relationship between coffee consumption and cardiovascular disease (7)  (8) . One of these studies showed that the lowest cardiovascular risk occurred with the consumption of 3 to 5 cups of coffee per day, and concluded that heavy coffee consumption was not associated with an elevated risk of cardiovascular disease (8) .
Caffeine and Glucose Metabolism. How does caffeine affect glucose metabolism? Well, one study evaluated the effect of consuming 200mg of caffeine taken twice per day for seven days on glucose metabolism, as well as on serum cortisol, DHEA, androstenedione, and nighttime salivary melatonin (9) . The study involved 16 healthy adults aged 18 to 22 with a history of caffeine consumption. The results of the study showed that the insulin levels were significantly higher, while insulin sensitivity was reduced. There were no differences in glucose, DHEA, androstenedione, and melatonin. Based on this study you would think that people with insulin resistance or type 2 diabetes should avoid drinking coffee, but a few studies have shown that coffee has a protective effect on the risk of type 2 diabetes, probably by affecting postprandial glucose homeostasis (10)  (11) .
Caffeine and Cortisol. One study measured the cortisol levels at eight times on days when healthy men and women consumed 250mg of caffeine 3x/day and underwent either mental stress or dynamic exercise protocols, followed by a midday meal (12) . The study showed that caffeine in combination with the mental stress further increased cortisol levels, whereas exercise alone didn’t increase cortisol, but caffeine taken before exercise elevated cortisol in both men and women. Another study looked to show whether tolerance develops with the daily intake of caffeine (13) . It involved 48 men and 48 women, and after five days of avoiding caffeine, challenges with caffeine caused a robust increase in cortisol across the test day. However, 5 days of consuming caffeine (300mg and 600 mg/day) abolished the morning cortisol response, although the cortisol levels were elevated later in the day. So the study showed that cortisol responses to caffeine are reduced, although not entirely eliminated, in healthy young men and women who consume caffeine on a daily basis.
Caffeine and the immune system. A number of in vitro and in vivo studies have demonstrated that caffeine modulates both the innate and adaptive immune responses (14) . Caffeine has been reported to decrease the production of both Th1 and Th2 cytokines (15) . Since these cytokines play a role in autoimmune conditions such as Graves’ Disease and Hashimoto’s Thyroiditis, it is possible that caffeine consumption can benefit many people with these conditions by decreasing pro-inflammatory cytokines. Another study showed that chronic caffeine treatment attenuates experimental autoimmune encephalomyelitis (15) . It might accomplish this by causing a shift in the Th1/Th2 pathways.
Caffeine and Sleep. One study evaluated the effects of 200mg and 400mg of caffeine on sleep in young and middle-aged adults (16) . The results of the study showed that compared to young adults, middle-aged adults are generally more sensitive to the effects of a high dose of caffeine on sleep quantity and quality (16) . However, another study found that low to moderate amounts of caffeine consumed in the home environment, mostly during morning hours, had little effect on sleep (17) . The ages of the participants ranged from 20 to 50 years.
Caffeine and Cancer. One study looked at the incidence of breast cancer in relation to caffeine consumption in Sweden (18) . The findings suggested that coffee consumption and caffeine intake is negatively associated with the risk of breast cancer, whereas tea consumption is positively associated with the risk of breast cancer (18) . Another study evaluated the association of caffeine and coffee consumption with regards to melanoma risk (19) . After adjustment for other risk factors, higher total caffeine intake was associated with a lower risk of melanoma (19) .
Caffeine and Alzheimer’s Disease. Numerous studies show that caffeine can have a protective effect against dementia and Alzheimer’s disease (20)  (21)  (22) . These studies were based specifically on the consumption of coffee, and one of the studies mentioned that 500mg of caffeine daily (equal to 4 or 5 cups of coffee per day) can protect against or treat Alzheimer’s disease (22) . Another one of these studies mentioned that the protective effects against cognitive decline/dementia are less evident in tea drinkers (21) .
Caffeine and Thyroid Health. There aren’t many studies which show a direct correlation between caffeine and thyroid health. I did come across a study which showed that coffee consumption may play a protective role against the development of benign or malignant thyroid neoplasms, possibly by the stimulatory effect of caffeine on the intracellular cyclic AMP production (23) . However, there is some evidence that coffee can interfere with the intestinal absorption of thyroid hormone medication (24) . This was based on a small study consisting of eight women, but it probably would be wise not to take thyroid hormone medication with coffee.
Genetic Polymorphisms and Caffeine Metabolism
Caffeine is metabolized by the cytochrome P450 1A2 (CYP1A2) enzyme. Many people have a genetic polymorphism for this enzyme, and those with certain genetic polymorphisms of the CYP1A2 enzyme are “rapid” caffeine metabolizers, whereas those with other genetic polymorphisms of the CYP1A2 enzyme are “slow” caffeine metabolizers (25) . So what does this mean? Well those people who are “rapid” caffeine metabolizers break down and excrete caffeine quickly, whereas those who are “slow” caffeine metabolizers break down and excrete caffeine slowly. Studies show that those who are slow metabolizers of caffeine have an increased risk of myocardial infarction (26)  and impaired fasting glucose (27) . So being a slow metabolizer of caffeine is associated with certain health risks, and while many people can tell this by the way they feel after consuming caffeine, some labs offer genetic testing available to confirm this.
How is this interpreted on an genetic lab report? Well, if you’re reading the interpretation from a 23andme test you should see CYP1A2 with an rsID listed as rs762551. You’ll also see a column that says “alleles”, which is what you want to pay attention to. If someone has the AA allele then they are considered to be a fast metabolizer (28) . If someone has the AC or CC allele then they are considered to be a slow metabolizer (28) .
Who Should Avoid Caffeine?
As I mentioned earlier, initially I recommend for just about all of my patients to avoid caffeine, especially in the form of coffee. Obviously not everyone takes my advice, although many people do. However, not everyone needs to avoid caffeine on a long-term basis. Those people who have adrenal problems will probably want to stay away from caffeine, at least until the health of their adrenals have been restored. And if someone is a slow metabolizer of caffeine then it also is a good idea to avoid consuming large amounts of caffeine.
When Can Caffeine Be Reintroduced?
Many people who eliminate caffeine from their diet eventually would like to reintroduce it. But when is the ideal time for someone to do this? Well, it does depend on the person. As I mentioned before, if someone has adrenal problems then it would be ideal for them to wait until the health of their adrenals have been restored before reintroducing caffeine. This is especially true with coffee since it is high in caffeine, but it probably is a good idea to limit one’s consumption of caffeine altogether until their adrenal health has significantly improved. If someone is a slow metabolizer of caffeine then it really is a good idea to minimize their consumption of caffeine on a permanent basis. This doesn’t mean that slow metabolizers can never drink coffee again, but it probably would be wise to limit your consumption if this is the case.
In summary, many people consume caffeine on a regular basis, and this of course includes people with thyroid and autoimmune thyroid conditions. Caffeine can have a negative effect on adrenal health, and thus probably should be avoided with those who have adrenal problems. On the other hand, caffeine modulates the immune system and might actually benefit some people with Graves’ Disease and Hashimoto’s Thyroiditis by decreasing pro-inflammatory cytokines. Coffee consumption might also decrease the risk of developing certain types of cancers. Since coffee can interfere with the intestinal absorption of thyroid hormone, if you are taking thyroid hormone medication it would be best not to consume coffee when taking this. Some people have a genetic polymorphism involving the CYP1A2 enzyme, and as a result can either be a “fast” metabolizer of caffeine, or a “slow” metabolizer of it. Those who are a “fast” metabolizer will be able to tolerate larger amounts of caffeine, whereas those who are “slow” metabolizers will have problems breaking down and excreting caffeine, and thus should minimize their consumption of it.