Which nutrient is poorly absorbed in achlorhydria (lack of stomach acid)?

Vitamin B12 is Poorly Absorbed in Achlorhydria

In achlorhydria (lack of stomach acid), vitamin B12 is poorly absorbed due to impaired release from food proteins and reduced intrinsic factor function. 1

Explanation of Achlorhydria and Its Impact on Nutrient Absorption

Achlorhydria is characterized by the absence of hydrochloric acid in gastric secretions, which significantly impacts the absorption of certain nutrients. This condition is commonly associated with:

• Atrophic gastritis, which can lead to increased risk of gastric cancer 2
• Helicobacter pylori infection 3
• Aging (hypochlorhydria is common in elderly populations) 1
• Use of medications such as proton pump inhibitors 4

Why Vitamin B12 Is Poorly Absorbed in Achlorhydria

Vitamin B12 absorption is uniquely affected by achlorhydria for several reasons:

• Stomach acid is required to release vitamin B12 from food proteins 4, 5
• Intrinsic factor, necessary for B12 absorption, functions optimally in an acidic environment 1
• Achlorhydria often coexists with atrophic gastritis, which reduces intrinsic factor production 6
• B12 absorption requires an acidic environment and presence of intrinsic factor produced by gastric parietal cells 1

Absorption Status of Other Listed Nutrients in Achlorhydria

Proteins (a)

• Protein digestion begins in the stomach with pepsin, which requires acid activation
• However, most protein digestion occurs in the small intestine via pancreatic enzymes
• While initial protein breakdown may be affected, overall absorption is not severely compromised 1

Fats (b)

• Fat absorption primarily occurs in the small intestine
• Stomach acid has minimal direct effect on fat absorption
• Pancreatic lipase and bile salts in the small intestine are the primary factors in fat digestion 1

Bile Salts (c)

• Bile salts are produced by the liver and stored in the gallbladder
• Their absorption occurs primarily in the terminal ileum
• Achlorhydria does not significantly impact bile salt absorption 1

Vitamin D (d)

• Vitamin D absorption occurs primarily in the small intestine
• While fat-soluble vitamin absorption can be somewhat affected by reduced fat digestion, vitamin D absorption is not severely compromised by achlorhydria alone 1

Vitamin B12 (e)

• Requires stomach acid to be released from food proteins
• Requires intrinsic factor (often reduced in conditions causing achlorhydria)
• Studies show high prevalence of B12 deficiency in patients with achlorhydria 1
• Even with supplementation, B12 absorption may be impaired in achlorhydria 6

Clinical Implications

The impaired absorption of vitamin B12 in achlorhydria has significant clinical implications:

• Vitamin B12 deficiency can lead to megaloblastic anemia and neurological complications 1
• Elderly patients with achlorhydria may require B12 supplementation via non-oral routes 4
• Monitoring of B12 status is recommended in patients with conditions associated with achlorhydria 1
• Oral B12 supplements at high doses may overcome malabsorption in some cases 4

Conclusion

Among the nutrients listed (proteins, fats, bile salts, vitamin D, and vitamin B12), vitamin B12 is the most significantly affected by achlorhydria due to its unique absorption mechanism requiring both stomach acid and intrinsic factor 1, 4.