What stops me from absorbing vitamin D? Uncovering the causes

December 18, 2025 •

2 min read

According to studies, vitamin D insufficiency affects a large percentage of the global population. Beyond insufficient sun exposure or diet, many people ask, 'what stops me from absorbing vitamin D?' The answer involves a complex web of medical conditions, lifestyle choices, and physiological processes that interfere with the body's ability to utilize this vital nutrient.

Quick Summary

Several factors can impede vitamin D absorption, including gastrointestinal disorders, impaired liver or kidney function, and excess body fat. Certain medications and genetic conditions can also disrupt vitamin D metabolism, making it difficult to maintain adequate levels and potentially leading to deficiency.

Key Points

Fat Malabsorption: Conditions like celiac, Crohn's, and cystic fibrosis prevent proper digestion and absorption of fat-soluble vitamin D.
Organ Impairment: Liver and kidney diseases interfere with the two-step process required to activate vitamin D for use in the body.
Obesity: Excess body fat can trap and sequester vitamin D, preventing it from circulating in the bloodstream.
Medications: Certain drugs, including steroids and anticonvulsants, can inhibit vitamin D absorption or accelerate its breakdown.
Genetic Factors: Rare inherited disorders can cause resistance to vitamin D, regardless of sufficient levels.
Lifestyle: Limited sun exposure due to geography, skin tone, or behavior is a major cause of insufficient vitamin D production.
Improve Absorption: Taking supplements with a fatty meal and ensuring adequate magnesium can enhance absorption.

Medical Conditions Impacting Absorption and Metabolism

Fat Malabsorption Syndromes

As vitamin D is a fat-soluble vitamin, its absorption is reliant on the body's ability to absorb dietary fats. Conditions that disrupt this can hinder vitamin D absorption, such as:

Celiac Disease
Crohn's Disease and Ulcerative Colitis
Cystic Fibrosis
Chronic Pancreatitis
Gastric Bypass Surgery

Impaired Liver and Kidney Function

Vitamin D requires metabolism by the liver and kidneys to become active. Issues with these organs disrupt this process.

Chronic Liver Disease can reduce the liver's ability to perform the first activation step.
Chronic Kidney Disease (CKD) impairs the final activation step in the kidneys.

Lifestyle and Environmental Factors

Obesity and Vitamin D Sequestration

Individuals with higher BMI often have lower vitamin D levels because the vitamin is stored in fat cells and less available to the body. This may necessitate higher supplementation doses.

Inadequate Sun Exposure

Sunlight is a key source of vitamin D. Factors limiting this include:

Geographic location
Extensive sunscreen use
Darker skin color
Limited time outdoors or covering most skin

Medications and Genetic Conditions

Medications That Interfere with Vitamin D

Certain drugs can impact vitamin D levels.


Medication Class	Example(s)	Mechanism of Interference
Anticonvulsants	Phenytoin, Phenobarbital	Accelerate vitamin D breakdown.
Corticosteroids	Prednisone, Dexamethasone	Impair vitamin D metabolism and reduce calcium absorption.
Bile Acid Sequestrants	Cholestyramine, Colestipol	Bind to bile acids needed for fat-soluble vitamin absorption.
Weight-Loss Drugs	Orlistat	Blocks fat absorption, reducing absorption of fat-soluble vitamins.

Genetic Predisposition

Rare genetic disorders can affect the body's response to vitamin D.

Vitamin D-Dependent Rickets Type I (VDDR1A) is caused by a gene mutation affecting activation.
Vitamin D-Resistant Rickets Type II (HVDRR) is due to a defective vitamin D receptor.

Improving Your Vitamin D Absorption

Consult a healthcare provider to diagnose and address vitamin D issues. General strategies include:

Taking supplements with a fatty meal to enhance absorption.
Optimizing magnesium intake, which is needed to activate vitamin D.
Treating underlying medical conditions.
Using special vitamin D forms under medical supervision for liver/kidney disease.
Discussing medication concerns with your doctor.

Conclusion

Poor vitamin D absorption has various causes, including medical conditions, obesity, and genetics. Consulting a healthcare professional for diagnosis and a personalized plan is the most effective approach. For more information, visit the National Institutes of Health fact sheet: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/.

Frequently Asked Questions

Yes, it is possible. Your body may not be properly absorbing or processing the vitamin D you get from sun exposure and food due to underlying medical conditions, genetic factors, or certain medications.

Yes, obesity can negatively affect your vitamin D levels. Excess body fat can sequester, or trap, vitamin D, preventing it from circulating freely in the bloodstream and reducing its bioavailability.

Medical conditions that cause malabsorption include inflammatory bowel diseases like Crohn's and celiac disease, cystic fibrosis, chronic pancreatitis, and a history of gastric bypass surgery.

Your liver and kidneys perform crucial steps in converting inactive vitamin D into its active form. Chronic disease in either organ can impair these processes, leading to a deficiency of active vitamin D.

Yes, taking your vitamin D supplement with a meal that contains healthy fats, such as avocado or nuts, can significantly improve its absorption because vitamin D is a fat-soluble vitamin.

Several medications can interfere with vitamin D, including certain corticosteroids (e.g., prednisone), anticonvulsants, bile acid sequestrants, and weight-loss drugs like Orlistat.

Rare genetic disorders, such as Vitamin D-dependent rickets, can cause defects in the enzymes that activate vitamin D or in the vitamin D receptor itself. These issues lead to a resistance to vitamin D's effects.

If you experience symptoms of vitamin D deficiency like bone pain, muscle weakness, or fatigue despite adequate intake, you may have an absorption issue. A doctor can order a blood test to check your levels and investigate potential causes.