As we wrote in our previous blog, there are many factors that affect the functioning of thyroid gland, ranging from seasonal changes to diet and medication. Thanks to new insights we have to add one major factor to the list: the intestinal flora. Intestinal flora and hormones The billions of micro-organisms residing in your intestines have a major impact on hormone production, including activity of the thyroid gland. This is no surprise in light of the recent insight that the intestinal flora appears to be connected to pretty much all vital body functions. T4 to T3 conversion Your gut microbes can recognize diverse hormonal substances including the adrenal hormones (adrenaline and noradrenaline) and thyroid hormones. They can and in fact do influence hormone metabolism. In the case of thyroid hormones, intestinal micro-organisms assist in the conversion of T4 to T3. About 20% of total body T4 is converted to T3 in the intestines. The digestive tract affects thyroid function Moreover, bile salts which end up in the small intestine after eating fats, have an influence on the thyroid gland, by way of triggering excretion of an enzyme that promotes the turnover of T4 to T3 (iodothyronine deiodinase). The digestive system is thus an integral part of the functioning of the thyroid gland. Closing "blind spot" in Western science Experts in the emerging field of "systems biology" argue for a better integration of the intestinal flora in effecting medical advances. The elimination of this notorious blind spot in modern Western science is long overdue, they argue. Only 1% human Because we carry approximately 20,000 human genes and approximately 2-20 million microbial genes at any time, "we" are only 1% human. Let this sink in: of all the genes we carry with us, only one hundredth is of homo sapiens origin. All other genes belong to microorganisms such as bacteria normally present on the skin or in the intestines. Ignoring this 99% of our internal and external "gene pool" is illogical for several vital reasons. Complex problems Increasing knowledge of this complex ecosystem in the gut does not make it any easier to comprehend. To understand the whole complex, high school biology does not get you far enough. Advanced “systems biology” approaches are increasingly required, and indeed increasingly central, to the life sciences and medical sciences in particular. Systems biology The whole is always greater than the sum of its parts. Systems biology is the study of live systems of biological components, which may be molecules, cells, organisms or entire species. Living systems are dynamic and complex, and their behavior may be hard to predict from the properties of individual parts. By monitoring and analyzing whole biological systems (using bioinformatics, biology, computer science, engineering and physics) knowledge is created that can predict how systems change over time. Intestinal flora as a solution It sometimes seems a more logical solution to look not in human genes but in the genetic make-up of the intestinal flora. This is obviously easier said than done. A paradigm shift is needed in the mindset of researchers and practitioners across many sciences dealing with nutrition, biology and medicine. Several factors As for the thyroid gland, it is important to know that the organ’s operation is not determined by a single system, but by many systems intricately linked together. These may be located in seemingly separate regions in the body, but are functionally closely associated with each other.