Hypothyroidism, Intestinal Bacterial Overgrowth, & Lactose Intolerance

Also see:
Autoimmunity and Intestinal Flora
Lactose Intolerance, Starch, Fructose, Sucrose, & Thyroid Status

“Bacterial overgrowth in the small intestine can be caused by hypothyroidism (Lauritano, et al., 2007), and the substances produced by these bacteria can damage the lining of the small intestine, causing the loss of lactase enzymes (Walshe, et al., 1990).” -Ray Peat, PhD

“The upper part of the small intestine is sterile in healthy people. In the last 40 years, there has been increasing interest in the “contaminated small-bowel syndrome,” or the “small intestine bacterial overgrowth syndrome.” When peristalsis is reduced, for example by hypothyroidism, along with reduced secretion of digestive fluids, bacteria are able to thrive in the upper part of the intestine. Sugars are very quickly absorbed in the upper intestine, so starches and fibers normally provide most of the nourishment for bowel bacteria…Thyroid hormone increases digestive activity, including stomach acid and peristalsis, and both thyroid and progesterone increase the ability of the intestine to absorb sugars quickly; their deficiency can permit bacteria to live on sugars as well as starches.” -Ray Peat, PhD

J Clin Endocrinol Metab. 2007 Nov;92(11):4180-4. Epub 2007 Aug 14.
Association between hypothyroidism and small intestinal bacterial overgrowth.
Lauritano EC, Bilotta AL, Gabrielli M, Scarpellini E, Lupascu A, Laginestra A, Novi M, Sottili S, Serricchio M, Cammarota G, Gasbarrini G, Pontecorvi A, Gasbarrini A.
OBJECTIVES:
Small intestinal bacterial overgrowth is defined as an abnormally high bacterial population level in the small intestine. Intestinal motor dysfunction associated with hypothyroidism could predispose to bacterial overgrowth. Luminal bacteria could modulate gastrointestinal symptoms and interfere with levothyroxine absorption. The aims of the present study were to assess the prevalence and clinical pattern of bacterial overgrowth in patients with a history of overt hypothyroidism and the effects of bacterial overgrowth decontamination on thyroid hormone levels.
METHODS:
A total of 50 consecutive patients with a history of overt hypothyroidism due to autoimmune thyroiditis was enrolled. Diagnosis of bacterial overgrowth was based on positivity to a hydrogen glucose breath test. Bacterial overgrowth positive patients were treated with 1,200 mg rifaximin each day for a week. A glucose breath test, gastrointestinal symptoms, and thyroid hormone plasma levels were reassessed 1 month after treatment.
RESULTS:
A total of 27 patients with a history of hypothyroidism demonstrated a positive result to the breath test (27 of 50, 54%), compared with two in the control group (two of 40, 5%). The difference was statistically significant (P < 0.001). Abdominal discomfort, flatulence, and bloating were significantly more prevalent in the bacterial overgrowth positive group. These symptoms significantly improved after antibiotic decontamination. Thyroid hormone plasma levels were not significantly affected by successful bacterial overgrowth decontamination.
CONCLUSIONS:
The history of overt hypothyroidism is associated with bacterial overgrowth development. Excess bacteria could influence clinical gastrointestinal manifestations. Bacterial overgrowth decontamination is associated with improved gastrointestinal symptoms. However, fermenting carbohydrate luminal bacteria do not interfere with thyroid hormone levels.

Gut. 1990 Jul;31(7):770-6.
Effects of an enteric anaerobic bacterial culture supernatant and deoxycholate on intestinal calcium absorption and disaccharidase activity.
Walshe K, Healy MJ, Speekenbrink AB, Keane CT, Weir DG, O’Moore RR.
Fifty two strains of anaerobic bacteria isolated from the upper gut of patients with small intestinal bacterial overgrowth were screened for phospholipase activity. Bacteroides melaninogenicus spp intermedius had the greatest activity. The effects of culture supernatants of this organism and deoxycholate on intestinal calcium absorption and disaccharidase activity were studied using a rat closed loop model. The supernatant decreased the in vitro uptake of calcium by 15% (p less than 0.001). Deoxycholate reduced calcium uptake by 16% (p less than 0.001). Combined culture supernatant and deoxycholate reduced calcium uptake by 39% (p less than 0.001) suggesting a potentiation of supernatant activity by deoxycholate. Culture supernatant and deoxycholate, both alone and combined, significantly reduced lactase, sucrase, and maltase activity. Electron microscopic evidence showed degeneration of microvilli, disruption of mitochondrial structure, and swelling of the endoplasmic reticulum after exposure of the intestinal loops to the supernatant or deoxycholate.