What Causes Vitamin D Deficiency Other Than Sunlight?

January 10, 2026 •

2 min read

While the sun is a primary source of vitamin D, a surprising number of people with ample sunlight exposure still suffer from low levels. This widespread issue, known as vitamin D deficiency, can be caused by a variety of factors unrelated to sun exposure, including underlying medical conditions, dietary choices, and even certain medications.

Quick Summary

Low vitamin D levels can result from various factors besides inadequate sun exposure, including poor dietary intake, impaired absorption due to gastrointestinal diseases, and decreased metabolism from liver or kidney disease. Certain medications, obesity, and genetics also contribute to vitamin D deficiency by affecting its synthesis, storage, or utilization.

Key Points

Malabsorption Syndromes: Conditions like celiac disease, Crohn's disease, and cystic fibrosis can prevent the small intestine from properly absorbing vitamin D from food and supplements.
Organ Function: Impaired liver or kidney function hinders the conversion of inactive vitamin D into its active, usable form, regardless of intake.
Obesity: Excess body fat can sequester vitamin D, preventing it from circulating freely in the bloodstream and leading to lower serum levels.
Medications: Certain drugs, including anti-seizure medications, steroids, and some cholesterol-lowering drugs, can interfere with vitamin D metabolism or absorption.
Limited Dietary Intake: A diet that lacks sufficient vitamin D from sources like fatty fish or fortified foods can lead to deficiency.
Genetic Factors: Some rare hereditary disorders can cause the body to resist the effects of vitamin D, even when levels appear normal.
Increased Need: Growing children and pregnant or breastfeeding women may have increased vitamin D requirements, increasing their risk for deficiency.

Malabsorption Issues

Vitamin D is absorbed in the small intestine. Certain gastrointestinal disorders can hinder this process, as vitamin D is fat-soluble and its absorption relies on proper fat absorption.

Celiac Disease: Damage to the small intestine from gluten intake reduces nutrient absorption.
Crohn's Disease: Inflammation of the digestive tract impairs nutrient uptake.
Cystic Fibrosis: Blocked pancreatic ducts impede fat and vitamin D absorption.
Bariatric Surgery: Procedures altering the digestive tract can impair nutrient absorption.

Impaired Metabolism and Function

Vitamin D requires conversion in the liver and kidneys to become active. Issues with these organs can lead to deficiency.

Liver Disease: Conditions like cirrhosis affect the first conversion step in the liver.
Kidney Disease: Chronic kidney disease prevents the final conversion in the kidneys.
Hereditary Disorders: Rare genetic conditions can cause resistance to vitamin D's effects.

Medications and Vitamin D

Some medications interfere with vitamin D metabolism and absorption, requiring monitoring for individuals on long-term treatment.

Anti-seizure Medications: Can increase vitamin D breakdown in the liver.
Corticosteroids: Can lower calcium absorption and disrupt vitamin D metabolism.
Cholesterol-Lowering Drugs: Some can interfere with fat-soluble vitamin absorption.
Weight-Loss Drugs: Medications reducing fat absorption can also inhibit dietary vitamin D uptake.

Obesity and Dietary Factors

Obesity and dietary choices also contribute to vitamin D deficiency.

Obesity

Obese individuals often have lower vitamin D levels, possibly because excess body fat sequesters the vitamin. Higher supplementation doses may be needed to achieve adequate levels.

Dietary Choices

Low intake of vitamin D-rich foods is a significant cause of deficiency.

Low Consumption of Rich Foods: Diets low in fatty fish, fish liver oils, or fortified products result in insufficient vitamin D.
Veganism: Strict vegan diets are at high risk unless fortified foods or supplements are used, as natural sources are mainly animal-based.

Comparison of Non-Sunlight Vitamin D Deficiency Causes

This table summarizes non-sunlight causes of vitamin D deficiency.


Cause	Mechanism	Impact on Body	At-Risk Individuals
Malabsorption	Diseases damaging intestinal lining prevent vitamin D absorption.	Reduced nutrient uptake, potential bone issues.	Individuals with GI diseases or bariatric surgery.
Impaired Metabolism	Liver or kidney disease prevents activation of vitamin D.	Low levels of active vitamin D, affecting bones and minerals.	Patients with chronic liver or kidney disease.
Medications	Drugs increase breakdown or block absorption.	Lowered vitamin D levels, potentially needing more supplements.	Those on certain long-term medications.
Obesity	Excess fat traps vitamin D.	Requires higher supplementation for adequate levels.	People with a BMI over 30.
Inadequate Diet	Low intake of rich or fortified foods.	Direct nutrient deficiency impacting health.	Vegans, vegetarians, limited diets.

Conclusion

Vitamin D deficiency is caused by more than just insufficient sun exposure. Various conditions can disrupt the body's absorption, metabolism, and use of vitamin D. These include gastrointestinal issues, liver and kidney problems, obesity, and specific medications. Understanding these diverse factors is vital for accurate diagnosis and effective treatment, which often requires more than just sun exposure to improve health outcomes.

Outbound link: What Causes Vitamin D Deficiency - MedlinePlus

Frequently Asked Questions

Yes, several digestive issues can cause vitamin D deficiency. Diseases such as celiac disease, Crohn's disease, and cystic fibrosis can impair the absorption of fat-soluble vitamins like D in the small intestine, leading to low levels.

Yes, obesity can significantly affect your vitamin D levels. Excess body fat can trap vitamin D and reduce the amount that circulates in the blood, often requiring higher doses of supplementation to correct the deficiency.

The kidneys play a crucial role in activating vitamin D. In cases of chronic kidney disease, the kidneys' ability to perform the final conversion step to the active form is diminished, leading to a deficiency.

Certain medications can interfere with vitamin D levels. Examples include anti-seizure drugs (like phenobarbital and phenytoin), corticosteroids (like prednisone), some cholesterol-lowering drugs, and specific weight-loss medications (like Orlistat).

Yes, it is possible to be deficient even with a healthy diet. This can happen if the diet is low in vitamin D-rich or fortified foods, if there are underlying malabsorption issues, or if certain medications are being taken.

Sunlight is a major factor, but it's not the only one because vitamin D must be absorbed from food and then metabolized by organs like the liver and kidneys to become active. Issues with any of these internal processes can cause a deficiency regardless of sun exposure.

You can check for vitamin D deficiency through a blood test that measures the concentration of 25-hydroxyvitamin D in your serum. A healthcare provider can order and interpret this test for you.