What Causes Your Body Not to Absorb Vitamin D?

October 28, 2025 •

3 min read

According to the Cleveland Clinic, a body mass index (BMI) over 30 is associated with lower vitamin D levels. This is just one of many factors that can impact nutrient uptake, prompting the question: what causes your body not to absorb vitamin D effectively?

Quick Summary

Several medical conditions, including gastrointestinal disorders, obesity, and liver or kidney disease, can significantly impair vitamin D absorption. Certain medications and lifestyle factors can also play a role in low vitamin D levels.

Key Points

Gastrointestinal Disorders: Conditions like Celiac disease, Crohn's disease, and cystic fibrosis can directly damage the intestinal lining, impairing fat and vitamin D absorption.
Obesity: Excess body fat can trap fat-soluble vitamin D, sequestering it from the bloodstream and leading to lower circulating levels, requiring higher doses to compensate.
Organ Function: Both the liver and kidneys are essential for converting vitamin D into its active form; dysfunction in these organs can severely hinder vitamin D metabolism.
Medication Interference: Certain drugs, including corticosteroids, some anti-seizure medications, and weight-loss drugs, can reduce vitamin D absorption or accelerate its breakdown.
Genetic Factors: Inherited genetic variations can influence the efficiency of vitamin D metabolism and the function of its receptors, causing individuals to absorb or activate the vitamin differently.
Improve Absorption with Fat: Taking oral vitamin D supplements with a fatty meal significantly enhances its absorption, as vitamin D is a fat-soluble nutrient.
Consider D3 over D2: If you use supplements, opt for vitamin D3 (cholecalciferol), as it is generally more effective at raising blood levels than vitamin D2.

The Vitamin D Pathway: From Sunlight to Absorption

Understanding how the body processes vitamin D is key to identifying absorption issues. Vitamin D is obtained from sunlight exposure and dietary sources. In the skin, UVB rays convert cholesterol into vitamin D3. Dietary vitamin D is absorbed in the small intestine. Both forms are transported to the liver, converted to 25-hydroxyvitamin D, and then to the active form, 1,25-dihydroxyvitamin D, in the kidneys. This active form is vital for calcium absorption. Problems at any point in this process can lead to deficiency.

Medical Conditions Affecting Vitamin D Absorption

Underlying health issues frequently interfere with vitamin D absorption or utilization. Gastrointestinal diseases that impair fat absorption are particularly common culprits.

Gastrointestinal Disorders

Certain conditions directly impact the small intestine's ability to absorb fat-soluble vitamins like vitamin D:

Celiac Disease: Damage from gluten hinders nutrient absorption.
Inflammatory Bowel Diseases (Crohn's, Ulcerative Colitis): Inflammation compromises intestinal absorption.
Cystic Fibrosis: Mucus blocks pancreatic enzymes needed for fat digestion and vitamin absorption.
Chronic Pancreatic Insufficiency: Lack of digestive enzymes impedes fat and vitamin D absorption.

Obesity and Weight Loss Surgery

Obesity (BMI > 30) is associated with lower vitamin D levels because excess fat tissue traps the vitamin, reducing its circulation. Gastric bypass surgery can cause malabsorption by altering the digestive tract and bypassing absorption sites in the small intestine.

Liver and Kidney Disease

These organs are vital for converting vitamin D to its active form.

Liver Disease: Impairs the first conversion step to 25-hydroxyvitamin D.
Kidney Disease: Hinders the final conversion to the active 1,25-dihydroxyvitamin D.

Medications and Genetic Factors

Some medications and genetic variations can also impact vitamin D status.

Medications: Drugs like corticosteroids, certain anti-seizure medications, cholesterol binders (cholestyramine), and the weight-loss drug orlistat can interfere with vitamin D metabolism or absorption.
Genetic Factors: Variations in genes like the vitamin D receptor (VDR) or those involved in metabolism (CYP2R1, CYP27B1) can affect how efficiently vitamin D is processed and utilized.

Comparison of Factors Affecting Vitamin D Absorption


Factor	Primary Mechanism of Impairment	Impact on Absorption	Potential Management Strategy
Gastrointestinal Disorders	Damage to intestinal lining or lack of digestive enzymes	Directly reduces absorption of dietary vitamin D	Manage underlying disease, potentially high-dose supplementation
Obesity	Sequestration of vitamin D in fat tissue	Reduces availability of stored vitamin D to the body	Higher vitamin D dosing to compensate for sequestration
Liver/Kidney Disease	Impairs conversion to active form	Indirectly reduces usable vitamin D	Specialized supplements or forms of vitamin D, medical management
Certain Medications	Speeds up vitamin D breakdown or blocks absorption	Reduces effective vitamin D levels	Consult with a doctor to adjust dosage or consider alternative medication

How to Improve Absorption if You Struggle

Improving vitamin D levels when absorption is an issue requires a tailored approach, often in consultation with a healthcare provider. Strategies depend on the underlying cause but may include:

Taking supplements with fat: Vitamin D is fat-soluble, so consuming supplements with a meal containing healthy fats improves absorption.
Ensuring adequate magnesium: Magnesium is needed to activate vitamin D in the body.
Addressing underlying conditions: Treating the primary health issue is crucial.
Choosing vitamin D3: This form is generally more effective at raising blood levels than D2.
Considering specialized formulas: For severe malabsorption, a doctor may recommend calcidiol or high-dose/injectable vitamin D, used with caution.

Conclusion

Beyond insufficient sun or diet, various medical conditions, medications, and genetic factors can cause your body not to absorb vitamin D effectively. Gastrointestinal disorders, obesity, liver and kidney disease, and certain drugs all interfere with the vitamin's absorption and metabolism pathway. Identifying and addressing these underlying issues with medical guidance is essential for managing low vitamin D levels. Strategies may involve targeted supplementation, dietary adjustments, and managing the primary health condition to improve vitamin D status and overall health.

Frequently Asked Questions

Yes, even with regular sun exposure, you can have a vitamin D deficiency. Factors like dark skin, use of sunscreen, or underlying medical conditions that interfere with your body's ability to synthesize or absorb vitamin D can still lead to low levels.

Obesity does not prevent your body from making vitamin D from the sun, but it does affect how it's used. Since vitamin D is fat-soluble, it gets stored and trapped in excess fat tissue, making less of it available for your body to use. People with a BMI over 30 often require higher vitamin D intake to maintain normal blood levels.

Several gastrointestinal issues can cause poor absorption, including Celiac disease, Crohn's disease, cystic fibrosis, and chronic pancreatitis. These conditions interfere with the digestion of fat, which is necessary for vitamin D absorption, or damage the intestinal lining where absorption occurs.

Yes, both liver and kidney function are critical. The liver performs the first step of converting vitamin D to a usable form, while the kidneys perform the second and final conversion into its active form. Disease in either organ can disrupt this process and lead to a deficiency.

Certain medications can interfere with vitamin D metabolism or absorption. These include some anti-seizure medications, corticosteroids, cholesterol-lowering drugs like cholestyramine, and the weight-loss drug orlistat.

Yes, it is recommended to take vitamin D supplements with a meal containing some fat. Because vitamin D is a fat-soluble vitamin, consuming it with dietary fats enhances its absorption into the bloodstream.

Your genetics can affect your vitamin D status through polymorphisms in the vitamin D receptor gene (VDR) or genes involved in its metabolism. These variations can impact how efficiently your body creates and processes vitamin D, potentially leading to lower levels even with adequate intake.

Yes, certain weight-loss surgeries, like gastric bypass, alter the digestive tract by bypassing a portion of the small intestine where vitamin D is absorbed. This can cause significant malabsorption and a need for lifelong supplementation.