Does Omeprazole Deplete Vitamin C? What the Research Says

Yes, omeprazole can deplete vitamin C, though the mechanism differs from its better-known effects on B12 and magnesium. Vitamin C exists in two forms in the stomach: ascorbic acid (the active, reduced form) and dehydroascorbic acid (the oxidized, less useful form). The acidic environment of a healthy stomach protects ascorbic acid from oxidation. When omeprazole raises gastric pH toward neutral, vitamin C oxidizes more rapidly, reducing the amount of bioavailable ascorbic acid reaching the small intestine for absorption. This effect is most relevant for people relying heavily on food-based vitamin C, as supplemental ascorbic acid taken on an empty stomach is absorbed before gastric pH becomes a major factor.

PubMed indexes 4,642 articles related to omeprazole's physiological effects, with multiple clinical trials measuring gastric and serum vitamin C levels in PPI users. Gastric juice vitamin C concentrations drop by 50-70% in patients taking omeprazole daily, according to endoscopic sampling studies. Serum vitamin C levels show a more modest but consistent decline of 10-20% in long-term users compared to controls. The CTD knowledge graph identifies 8 genes in the vitamin C metabolism pathway (including SLC23A1 and SLC23A2 transporters) that interact with compounds modulated by acid suppression. ChEMBL documents 402 compounds that modulate the ascorbate metabolism pathway, providing molecular context for how gastric pH changes cascade into altered vitamin C homeostasis. The clinical significance is greatest in populations with marginal vitamin C intake.

Omeprazole raises gastric pH from its normal range of 1-2 to approximately 4-6 by irreversibly inhibiting the proton pump on parietal cells. At this higher pH, ascorbic acid rapidly oxidizes to dehydroascorbic acid, which has reduced bioavailability and is less efficiently absorbed by the sodium-dependent vitamin C transporters (SVCT1 and SVCT2) in the intestinal lining. The stomach normally acts as a protective reservoir that maintains vitamin C in its reduced form until it reaches the duodenum for absorption. Omeprazole effectively removes this protective acid environment. Additionally, reduced gastric acidity promotes overgrowth of bacteria that can further consume vitamin C before it reaches absorptive surfaces. The effect compounds over time, particularly in individuals with limited dietary vitamin C intake or those taking omeprazole at higher doses.

If you take omeprazole long-term, increasing your vitamin C intake is a straightforward countermeasure. Supplementing with 250-500 mg of ascorbic acid daily, taken on an empty stomach at least 30 minutes before omeprazole, allows absorption before acid suppression takes full effect. Citrus fruits, bell peppers, strawberries, and broccoli provide food-based vitamin C, though absorption from food will be partially compromised by the elevated gastric pH. Consider spacing vitamin C-rich foods away from your omeprazole dose when possible. Unlike B12 depletion, vitamin C depletion from PPIs is typically moderate and rarely causes scurvy in well-nourished individuals. However, suboptimal vitamin C levels can impair immune function, wound healing, and iron absorption over time. Periodic assessment of vitamin C status may be worthwhile for long-term PPI users.