Caffeine consumption may improve thyroid function for people with metabolic disorders, new research shows.
"Although the causal relationship between caffeine intake and thyroid function requires further verification, as an easily obtainable and widely consumed dietary ingredient, caffeine is a potential candidate for improving thyroid health in people with metabolic disorders," report the authors in the study, published in Nutritional Journal.
Caffeine intake, within established healthy ranges, showed a nonlinear association with thyroid levels.
Moderate caffeine intake has been associated with reducing the risk of metabolic disorders in addition to showing some mental health benefits. However, research on its effects on thyroid hormone, which importantly plays a key role in systemic metabolism and neurologic development, is lacking.
To investigate the effects, Yu Zhou, of the Department of Rehabilitation Medicine, School of Health, Fujian Medical University, Fuzhou, China, and colleagues evaluated data from the National Health and Nutrition Examination Survey (NHANES) III 2007–2012 study involving 2582 participants for whom data were available regarding medical conditions, dietary intake, thyroid function, and demographic background.
The participants were divided into three subgroups based on sex, age, body mass index (BMI), hyperglycemia, hypertension, and cardio-cerebral vascular disease (CVD).
Group 1 (n = 208) was the most metabolically unhealthy. Patients in that group had the highest BMI and were of oldest age. In addition, that group had higher rates of hypertension, hyperglycemia, and CVD, but, notably, it had the lowest level of caffeine consumption.
In group 2 (n = 543), all participants were current smokers, and 90.4% had a habit of drinking alcohol. That group also had the highest percentage of men.
Group 3 (n = 1183) was the most metabolically healthy, with more women, younger age, and lowest BMI. No participants in that group had hyperglycemia, hypertension, or CVD.
Group 1, the most metabolically unhealthy, had the highest serum thyroid-stimulating hormone (TSH) levels. Of note, while participants with thyroid diseases were initially excluded from the analysis, higher TSH levels are predictive of subclinical hypothyroidism or progression to overt hypothyroidism.
Overall, there was no association between caffeine and TSH levels.
However, a subgroup analysis of the groups showed that in group 1, caffeine intake correlated with TSH nonlinearly (P = .0019), with minimal average consumption of caffeine (<9.97 mg/d). There was an association with slightly higher TSH levels (P = .035) after adjusting for age, sex, race, drink, disease state, micronutrients, and macronutrients.
However, in higher, moderate amounts of caffeine consumption (9.97–264.97 mg/d), there was an inverse association, with lower TSH (P = .001).
Interestingly, there was no association between daily caffeine consumption of more than 264.97 mg and TSH levels.
For context, a typical 8-ounce cup of coffee generally contains 80 to 100 mg of caffeine, and the US Food and Drug Administrationindicates that 400 mg/d of caffeine is safe for healthy adults.
Group 2 consumed the highest amount of caffeine. Notably, that group had the lowest serum TSH levels of the three groups. There were no significant associations between caffeine consumption and TSH levels in group 2 or group 3.
There were also no significant associations between caffeine consumption and levels of serum FT4 or FT3, also linked to thyroid dysfunction, in any of the groups.
The findings show that "caffeine consumption was correlated with serum TSH nonlinearly, and when taken in moderate amounts (9.97– 264.97 mg/d), caffeine demonstrated a positive correlation with serum TSH levels in patients with metabolic disorders," the authors conclude.
Mechanisms?
Caffeine is believed to modulate pituitary hormone secretion, which has been shown to influence the hypothalamic-pituitary-adrenal axis. The authors speculatethat caffeine could potentially affect thyroid activity by affecting pituitary function.
"However, the effects of transient and chronic caffeine administration on human thyroid function need to be verified further, and the related mechanisms remain unclear," they note.
Commenting on the study, Maik Pietzner, PhD, of the Berlin Institute of Health, Berlin, Germany, notes that an important limitation of the study is that various patient groups were excluded, including those with abnormal TSH levels.
"What makes me wonder is the high number of exclusions and the focus on very specific groups of people. This almost certainly introduces bias, eg, what is specific to people not reporting coffee consumption," Pietzner said.
Furthermore, "we already know that patients with poor metabolic health do also have slight variations in thyroid hormone levels and also have different dietary patterns," he explained.
"So reverse confounding might occur in which the poor metabolic health is associated with both poor thyroid hormone levels and coffee consumption," Pietzner said.
He also notes the "somewhat odd" finding that the group with the highest metabolic disorders had the lowest coffee consumption, yet the highest TSH levels.
"My guess would be that this might also be a chance finding, given that the distribution of TSH values is very skewed, which can have a strong effect in linear regression models," Pietzner said.
In general, "the evidence generated by the study is rather weak, but there is good evidence that higher coffee consumption is linked to better metabolic health, although the exact mechanisms is not known, if indeed causal," Pietzner added.
"Prospective studies are needed to evaluate whether higher coffee consumption indeed lowers the risk for thyroid disease."
NutrJ. Published July 26, 2023. Abstract
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