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Vitamin B12 and Thyroid Deficiency

By Jacob Schor, ND, FABNO

People who take thyroid hormone supplementation are often still tired. They come to us because their doctors tell them their TSH is fine and there's nothing more to be done. We try them on "natural thyroid," give them active hormone, support their adrenal function and do a host of other things that sometimes work. We may be going about this the wrong way. Here's where I am these days.

First off, test run a serum vitamin B12 level and an iron panel. A surprisingly high percentage of patients will be deficient in one or both. A 2006 paper by Ness-Abramof, et al., was the first I read describing the association between vitamin B12 deficiency and autoimmune thyroid disease (AITD).12 Of the 115 people in the study, all of whom had AITD, 32 (28 percent) had low vitamin B12 levels. Of those patients who were B12 deficient, 31 percent had pernicious anemia.

The most common cause of B12 deficiency is atrophic gastritis, a condition that damages the parietal cells, preventing them from making intrinsic factor, leading to pernicious anemia. Atrophic gastritis is typically the result of an autoimmune process in which the immune system inappropriately attacks the parietal cells or intrinsic factor itself. Approximately 90 percent of individuals with pernicious anemia have antibodies for parietal cells; however, only 50 percent of individuals with these antibodies have pernicious anemia.

Ness-Abramof, et al., were not the first to report an association between autoimmune thyroid disease and B12 deficiency. An Italian study reported that 22 of 62 AITD patients had confirmed atrophic gastritis.5 Antiparietal cell antibodies were found in 68 percent (15/22) of patients with atrophic gastritis. Anemia was observed in 82 percent (18/22) of patients with AITD and atrophic gastritis.

It turns out that it's not just autoimmune thyroid disease that is associated with low iron. Any hypothyroid patient may be B12 deficient. Jabbar, et al., tested 116 hypothyroid patients and found that 46 (39.6 percent) of them had low vitamin B12 levels.10

Presence or absence of thyroid antibodies did not hint to B12 deficiency risk. In the Ness-Abramof, et al., paper, the researchers only looked at people with autoimmune thyroid disease.12 Approximately the same percentage of patients with positive thyroid antibodies were B12 deficient (43.2 percent) as those with negative antibodies (38.9 percent).

Something else stands out in the Centanni, et al., study.5 Without testing their blood for B12 levels, it was hard to pick out which patients were deficient. The classic signs and symptoms we expect to see with B12 deficiency were little help in identifying affected individuals. That makes sense, symptom-wise, as both conditions leave the person weak, foggy-brained, depressed and with dulled reflexes. Vitamin B12 deficiency also causes numbness, but the differences in presentation were not significant.

The mean corpuscular volume (MCV), which we assume should increase with B12 deficiency, did not differ between groups. Nor were the B12-deficient patients more likely to be anemic.

So, depending on which paper you read, 30-40 percent of people being treated for low thyroid are B12 deficient.

You need to test for iron as well. Autoimmune thyroid patients have a high incidence of iron deficiency.5 There are a few possible explanations for this. First, the autoimmune activity in their body may not be limited to attacking their thyroid. It may also attack the parietal cells in the stomach, causing atrophic gastritis. Atrophic gastritis causes about one-quarter of all cases of chronic iron-deficiency anemia. Atrophic gastritis can trigger both iron deficiency and B12 deficiency.8,9

What happens on the CBC when someone is both iron and B12 deficient? Vitamin B12 deficiency causes macrocytic anemia and the MCV increases. If B12 and iron deficiencies coexist, the combined increased MCV caused by B12 deficiency and the decreased MCV caused by iron deficiency and cancel each other out. The MCV may look normal. The only hint on the CBC may be a larger RDW.

Several diseases are closely related. One in four people who make antibodies that attack their thyroid also make antibodies that attack the parietal glands, and this can cause B12 and iron deficiency. This probably explains why so many hypothyroid patients find relief taking digestive enzymes.

Then there is celiac disease. People with celiac disease have a higher-than-normal incidence of AITD, about twice the expected. It works both ways; people with thyroid disease are also more likely to have celiac disease.7 Celiac disease also increases risk of B12 deficiency. In one study, 12 percent of celiac patients were B12 deficient.6

People with iron deficiency, B12 deficiency anemia or low thyroid function all complain about the same thing. All three conditions cause fatigue. Vitamin B12 deficiency may also cause neurologic symptoms, typically peripheral glove and stocking numbness or neuropathy. H. pylori infection presents with upper GI symptoms.1,2

There is something else we need to check with hypothyroid patients. There are a number of substances that interfere with thyroid hormone absorption. These include iron, calcium and chromium supplements. People may be taking them with their thyroid medication and not realize they block absorption. A particularly sneaky absorption blocker is coffee. Hypothyroid patients tend to be tired, especially if they are also anemic. They will often tell you that a morning cup (or pot) of coffee is essential. Coffee lowers thyroid hormone absorption by about a third.3 I've started telling my coffee-drinking hypothyroid patients to take their thyroid at night. It's actually better absorbed that way.4

There's been a long tradition of switching people from synthetic T-4 thyroid hormone to naturally derived combinations of T-4 and T-3. Lately, it's become common to use synthetic combinations of T3 and T-4. There are various theories to justify doing this. The most popular explanation is that due to inadequate conversion of T-4 to T-3, the patient still feels tired. Siegmund, et al., compare duo thyroid hormone therapies against traditional T-4 monotherapy and tell us that it doesn't help the patient feel better: "Replacement therapy of hypothyroidism with T4 plus T3 does not improve mood and cognitive performance compared to the standard T4 monotherapy."13

These recent papers point to the high probability that people who are hypothyroid may have one or more coexistent conditions that could also be causing fatigue. Don't expect any of the classic hints of B12 deficiency. Their MCV may be normal. They may not have anemia or numbness. They may just complain of tiredness that hasn't been helped by their thyroid medicine. There are people who have all three: low thyroid, B12 deficiency and iron deficiency. Once you start looking, you find them more often than you would think.


  1. Annibale B, et al. Atrophic body gastritis: distinct features associated with Helicobacter pylori infection. Helicobacter, June 1997;2(2):57-64.
  2. Annibale B, et al. Cure of Helicobacter pylori infection in atrophic body gastritis patients does not improve mucosal atrophy but reduces hypergastrinemia and its related effects on body ECL-cell hyperplasia. Aliment Pharmacol Ther, May 2000;14(5):625-34.
  3. Benvenga S, et al. Altered intestinal absorption of L-thyroxine caused by coffee. Thyroid, March 2008;18(3):293-301.
  4. Bolk N, et al. Effects of evening vs. morning thyroxine ingestion on serum thyroid hormone profiles in hypothyroid patients. Clin Endocrinol (Oxf), January 2007;66(1):43-8.
  5. Centanni M, et al. Atrophic body gastritis in patients with autoimmune thyroid disease: an underdiagnosed association. Arch Intern Med, Aug. 9-23, 1999;159(15):1726-30.
  6. Dickey W. Low serum vitamin B12 is common in coeliac disease and is not due to autoimmune gastritis, Eur J Gastroenterol Hepatol, April 2002;14(4):425-7.
  7. Hadithi M, et al. Coeliac disease in Dutch patients with Hashimoto's thyroiditis and vice versa. World J Gastroenterol, March 21, 2007;13(11):1715-22.
  8. Hershko C, et al. The anemia of achylia gastrica revisited. Blood Cells Mol Dis, Sep-Oct 2007;39(2):178-83.
  9. Hershko C, et al. Role of autoimmune gastritis, Helicobacter pylori and celiac disease in refractory or unexplained iron deficiency. Haematologica, May 2005;90(5):585-95.
  10. Jabbar A, et al. Vitamin B12 deficiency common in primary hypothyroidism. J Pak Med Assoc, May 2008;58(5):258-61.
  11. Marcoullis G, et al. Cobalamin malabsorption due to nondegradation of R proteins in the human intestine. Inhibited cobalamin absorption in exocrine pancreatic dysfunction, J Clin Invest, September 1980;66(3):430-40.
  12. Ness-Abramof R, et al. Prevalence and evaluation of B12 deficiency in patients with autoimmune thyroid disease. Am J Med Sci, September 2006;332(3):119-22.
  13. Siegmund W, et al. Replacement therapy with levothyroxine plus triiodothyronine (bioavailable molar ratio 14:1) is not superior to thyroxine alone to improve well-being and cognitive performance in hypothyroidism. Clin Endocrinol (Oxf), June 2004;60(6):750-7.
  14. Tomasi PA, et al. Is there anything to the reported association between Helicobacter pylori infection and autoimmune thyroiditis? Dig Dis Sci, February 2005;50(2):385-8.

About the Author: Dr. Jacob Schor graduated with a bachelor of science degree from Cornell University and received his naturopathic training at National College of Naturopathic Medicine. He currently practices at the Denver Naturopathic Clinic. He is the legislative chair for the Colorado Association of Naturopathic Physicians (CANP), and is on the board of directors and secretary of the Oncology Association of Naturopathic Physicians. E-mail Dr. Schor at

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Date Last Modified - Friday, 17-Oct-2008 12:11:20 PDT