Why am I not absorbing vitamin D properly? Exploring the reasons behind poor absorption

December 12, 2025 •

4 min read

An estimated 42% of adults in the United States are deficient in vitamin D, a condition that is often overlooked and can lead to serious health issues. For some, a deficiency isn't a matter of insufficient intake but an inability to absorb it, leaving many to wonder, "Why am I not absorbing vitamin D properly?".

Quick Summary

Poor vitamin D absorption can result from underlying medical conditions, such as Crohn's disease and bariatric surgery, certain medications, aging, and obesity. Strategies like taking supplements with high-fat meals can help improve vitamin D uptake.

Key Points

Underlying Medical Conditions: Conditions like celiac disease, Crohn's, and cystic fibrosis can damage the intestinal lining and prevent proper vitamin D absorption.
Bariatric Surgery: Weight-loss procedures that alter the digestive tract can bypass sections of the intestine responsible for nutrient absorption.
Lifestyle and Dietary Factors: Obesity can trap vitamin D in fat tissue, while a diet lacking sufficient fat can hinder its absorption.
Aging and Medications: The ability to absorb vitamin D can decrease with age, and certain medications can interfere with its metabolism.
Genetics Can Play a Role: Genetic variations can affect the synthesis and transport of vitamin D, impacting an individual's overall status.
Improve Absorption with Meals: Taking vitamin D supplements with high-fat meals can significantly boost absorption rates.

The Crucial Role of Vitamin D

Vitamin D is a fat-soluble vitamin essential for regulating calcium and phosphate in the body, which helps maintain strong bones and proper muscle function. It is also critical for immune function, mood regulation, and fighting infection. While many people get their vitamin D from sunlight exposure and fortified foods, these sources are insufficient for some due to a variety of factors, including malabsorption issues.

Medical Conditions Affecting Vitamin D Absorption

Several underlying health issues can interfere with your body's ability to absorb vitamin D, particularly conditions that impact fat absorption. Because vitamin D is fat-soluble, its uptake depends on the presence of fats in the diet and a healthy digestive tract.

Digestive and Pancreatic Disorders

Celiac Disease: An autoimmune disorder where consuming gluten damages the lining of the small intestine. This damage reduces the surface area available for absorbing nutrients, including vitamin D.
Crohn's Disease and Ulcerative Colitis: These inflammatory bowel diseases cause inflammation and scarring in the small intestine, significantly hindering nutrient absorption.
Cystic Fibrosis: A genetic disorder causing the body to produce thick, sticky mucus. This mucus can block ducts in the pancreas, preventing digestive enzymes necessary for fat absorption from reaching the small intestine.
Exocrine Pancreatic Insufficiency (EPI): A condition where the pancreas does not produce enough of the enzymes needed to digest food, including fats. Without these enzymes, vitamin D cannot be properly absorbed.

Weight-Loss (Bariatric) Surgery

Bariatric procedures, such as gastric bypass surgery, intentionally alter the digestive tract to promote weight loss. These changes, particularly those that bypass a portion of the small intestine, can severely limit the area available for nutrient absorption, including vitamin D. Long-term monitoring and supplementation are crucial for these patients.

Liver and Kidney Disease

The liver and kidneys play a critical role in converting vitamin D into its active form. Liver disease can impair the initial processing of vitamin D, while kidney disease can disrupt its final conversion, leading to deficiency even with adequate intake.

Lifestyle and Other Factors

Beyond medical conditions, several other factors can influence how well your body absorbs vitamin D.

Comparison of Factors Affecting Vitamin D Absorption


Factor	Impact on Absorption	Details
Obesity	Reduced	Body fat can sequester or trap vitamin D, preventing it from circulating freely in the bloodstream.
Age	Reduced	As we age, our skin's ability to produce vitamin D from sunlight decreases. The gut may also absorb less efficiently over time.
Medications	Can reduce	Certain drugs, including some steroids, laxatives, and cholesterol-lowering medications, can interfere with vitamin D metabolism.
Lack of Dietary Fat	Reduced	Because vitamin D is fat-soluble, a very low-fat diet can hinder absorption from food and supplements.
Genetics	Variable	Genetic variations in genes related to vitamin D synthesis and transport can influence an individual's vitamin D status.

Dietary Considerations

Vitamin D is a fat-soluble vitamin, meaning it is absorbed most efficiently with dietary fat. Studies have shown that taking vitamin D supplements with the largest meal of the day, which is more likely to contain fat, can significantly improve absorption. Incorporating healthy fats from sources like avocados, nuts, seeds, and fatty fish can aid in this process.

How to Improve Your Vitamin D Absorption

If you have concerns about malabsorption, several steps can help, but it's essential to consult a healthcare provider for a proper diagnosis and treatment plan.

Here are some strategies to discuss with your doctor:

Optimize Supplement Timing: Take your vitamin D supplement with a meal that contains healthy fats to maximize absorption.
Consider Vitamin D3: Research suggests that vitamin D3 is more effective than D2 at raising and sustaining blood levels.
Address Underlying Conditions: Working with a doctor to manage and treat conditions like celiac or Crohn's disease is critical for improving overall nutrient absorption.
Get Screened Regularly: Individuals with high-risk factors, such as older adults, those with digestive disorders, or people who have undergone bariatric surgery, should be monitored regularly to track their vitamin D levels.

Conclusion

Poor vitamin D absorption is a complex issue with a range of possible causes, from gastrointestinal disorders to lifestyle factors. By understanding the root causes, individuals can work with healthcare providers to develop an effective strategy to address the deficiency. Simply taking more supplements may not be the answer if an underlying condition is preventing proper uptake. Focusing on optimizing supplement timing, choosing the right form of vitamin D, and addressing any medical issues is key to restoring healthy vitamin D levels. The path to better health begins with identifying why your body isn't effectively absorbing this vital nutrient.

For more detailed information on problems with digestion and absorption, particularly following bariatric surgery, you can visit Johns Hopkins Medicine.

Frequently Asked Questions

Medical conditions that cause vitamin D malabsorption include inflammatory bowel diseases like Crohn's and ulcerative colitis, celiac disease, cystic fibrosis, and exocrine pancreatic insufficiency, all of which disrupt normal fat and nutrient absorption in the gut.

Yes, obesity can negatively affect vitamin D absorption because body fat can sequester, or trap, vitamin D, making it less available for use by the body. This often requires higher doses of vitamin D to maintain adequate blood levels.

Yes, some medications can interfere with vitamin D absorption and metabolism. Examples include certain steroids, laxatives, and some cholesterol-lowering drugs. You should always discuss your medications with a healthcare provider.

To naturally improve absorption, ensure you consume adequate healthy fats from sources like avocados, nuts, and fish. Also, timed sun exposure can help your body produce vitamin D, though caution is needed with prolonged exposure.

Research indicates that vitamin D3 (cholecalciferol) is typically absorbed more effectively and raises blood levels of vitamin D higher and for longer than vitamin D2 (ergocalciferol).

After bariatric surgery like gastric bypass, the digestive tract is altered to bypass part of the small intestine. This significantly reduces the area where vitamin D is normally absorbed, leading to a high risk of deficiency.

Symptoms of poor absorption are the same as vitamin D deficiency and can include fatigue, bone and muscle pain, hair loss, a depressed mood, and frequent infections.

Yes, older adults have a reduced capacity for synthesizing vitamin D from sun exposure. Additionally, some studies suggest that intestinal absorption of vitamin D may decrease with age.