Study under review: Effect of Excessive Green Tea versus Fluoride and Caffeine on Body Weight and Serum Thyroid Hormones in Male Mice
Tea is the most popular beverage in the world after water. While there are many kinds of herbal infusions, actual teas are made from the leaf of Camellia sinensis. Based on the level of processing, teas are classified principally as black (fermented), oolong (semi-fermented), or green (unfermented). In recent years, there has been a growing demand for tea, with worldwide consumption increasing to 4.84 million tons in 2013.
In addition to the surge of people looking to quench their thirst, there has been growing interest in the potential health benefits of tea, especially green tea. For instance, it has been estimated (from observational studies) that the risk of dying from any cause is reduced by 4% with each additional cup of green tea consumed daily. The leaves of Camellia sinensis are a complex mix of proteins and free amino acids, carbohydrates, fats, minerals, and most importantly, polyphenols. Most of those polyphenols are catechins, the major ones being epicatechin, epigallocatechin, epicatechin-3-gallate, and epigallocatechin-3-gallate (EGCG). All have been studied extensively for their potential role in the prevention of some chronic diseases and for their contribution to general health.
However, it is not far-fetched to believe that benefits only exist up to a certain dose, above which adverse effects might occur. For example, previous research has suggested that daily green tea consumption can induce hypothyroidism in rats by interfering with the thyroid gland’s use of iodine to make thyroid hormones (T4 and T3). Studies in northern Europe, Japan, and the U.S. have found the prevalence of spontaneous hypothyroidism to be between 1% and 2% in iodine-replete humans. Green tea is one of the most popular beverages in the world. Could it be contributing to this phenomenon?
The potential link between green tea and thyroid function could be owed to any number of compounds within green tea. In addition to the catechins, green tea contains variable amounts of fluoride and 30-60 milligrams of caffeine per cup (eight ounces), both of which are dependent on the plant’s growing conditions. An association between hypothyroidism and the fluoride content of drinking water has been established, and animal research has shown that excessive fluoride inhibits thyroid hormone production. Animal research has also shown that excessive caffeine consumption induces hypothyroid effects that may be synergistic with iodine deficiency. In the current study, the potential effects of green tea on thyroid function were studied and compared to those of two of its components, fluoride and caffeine, to determine potential adverse effects.
Green tea had been studied extensively for its health benefits, but sometimes there can be too much of a good thing. The purpose of this study was to determine if higher doses of green tea could adversely affect thyroid function in mice. Fluoride and caffeine, both found in green tea, were also examined in parallel to see how their effects compared to green tea.
Other Articles in Issue #11 (September 2015)
A shot to the gut
Alcohol intake and gut impacts have been researched before, but we still aren’t sure what exactly goes on after people drink. This study looked at what happens with gut bacterial products when people have multiple drinks at one sitting ... aka “binge drinking”.
Tea time means only tea for optimal EGCG absorption
Many people drink green tea for health, and some take green tea or EGCG supplements in an attempt to shed extra fat. While these topics have been researched at length, there hasn’t been as much research on timing. This study looks at EGCG absorption with and without food.
Can omega-3s prevent cognitive decline?
One of the most important issues with aging is decreased cognitive ability and eventually dementia. Since the brain has such high omega-3 content, many people supplement for prevention of these issues. This large, multi-year study put that practice to the test.
The study that didn’t end the low-fat/low-carb diet “wars”
A recent metabolic ward study set the low-carb world on fire, and produced many inaccurate media headlines disparaging low-carb diets. We cover the study and its implications, detail by detail.
- Interview: Dylan Dahlquist, MSc(c)
When is breakfast the most important meal of the day?
With an increasing amount of research pointing to benefits of intermittent fasting, breakfast has been shunned by more and more people. But for those with type 2 diabetes, blood sugar is a central issue, and breakfast may play a major role in regulating it.
What to Expect When We’re Expecting: Fetal Programming and the Development of Taste Preferences
By Margaret Leitch, Ph.D.
Gluten-intolerant? There’s a pill for that
Some people are lactose intolerant, but still drink milk thanks to the availability of lactase enzymes. That setup isn’t yet possible for those who don’t handle gluten well. This study examines the efficacy of a promising enzymatic adjunct to a gluten-free diet.
Vitamin D(efense) against Crohn’s disease?
Immune benefits are often listed among the multitude of possible vitamin D effects. Most of the time, this is simplified to “defense against colds and flu”. But many conditions have an immune component — this particular study examines potential mechanisms by which vitamin D may help Crohn’s disease.