In addition to blocking absorption of thyroid hormone and increasing the risk of osteoporosis, acid blockers like Prilosec and Nexium can cause vitamin B12 deficiency. Although acid blockers and antacids are OK for short term or occasional use, natural alternatives can heal indigestion by restoring healthy digestion so you can stop the acid blockers comfortably.
In this study, involving subjects aged 60-102 years, prolonged use of proton-pump inhibitors (PPI) like Prilosec, Nexium and Prevacid were associated with a significant decline in serum vitamin B12 levels.This did not correct even when RDA levels of B12 were given. Fortunately, Tagamet and Zantac (H2 Blockers) did not cause B12 deficiency.
The authors of this study conclude, "B12 status declines during prolonged PPI use in older adults, but not with prolonged H2 blocker use; supplementation with RDA amounts of B12 do not prevent this decline. This report reinforces that B12 deficiency is common in the elderly and suggests that it appears prudent to monitor periodically B12 status while on prolonged PPI use, to enable correction before complications ensue."
The 500 mcg of vitamin B12 in a good multivitamin powder is enough to prevent and correct the B12 deficiency, as if results in significant absorption even in the absence of stomach acid.
"Do Acid-lowering agents affect Vitamin B12 status in older adults?" Dharmarajan TS, Norkus EP, et al, J Am Med Dir Assoc, 2008; 9(3): 162-7.