What Causes Lack of Vitamin D Deficiency?

October 27, 2025 •

2 min read

Globally, more than a billion people are estimated to have inadequate vitamin D levels. Understanding what causes lack of vitamin D deficiency is crucial, as this condition can lead to significant health problems, including weakened bones and impaired immune function. Low vitamin D can stem from a variety of factors, from environmental conditions to underlying health issues, affecting people of all ages and backgrounds.

Quick Summary

This article explores the multiple contributing factors that can lead to inadequate vitamin D levels, covering the role of sunlight, dietary intake, underlying health conditions, body weight, and specific medications. It also discusses populations at higher risk and offers a comparison of how different factors impact deficiency.

Key Points

Limited Sunlight Exposure: Insufficient exposure to ultraviolet B (UVB) radiation from the sun is the most common cause of vitamin D deficiency, especially in higher latitudes, during winter, and for those who spend most of their time indoors.
Increased Skin Melanin: People with darker skin pigmentation have more melanin, which reduces the skin's ability to produce vitamin D from sunlight, increasing their risk of deficiency.
Poor Dietary Intake: Few foods naturally contain vitamin D, and a diet lacking fatty fish, eggs, and fortified products can lead to inadequate intake.
Malabsorption Disorders: Medical conditions affecting the gut, such as celiac disease, Crohn's disease, and cystic fibrosis, can prevent the proper absorption of fat-soluble vitamin D.
Obesity: Higher body fat levels are associated with lower vitamin D, as adipose tissue can sequester and trap the vitamin, keeping it from circulating in the bloodstream.
Chronic Kidney and Liver Disease: These conditions impair the organs' ability to convert vitamin D into its active, usable form, disrupting the body's metabolic process.
Certain Medications: Drugs like steroids, anticonvulsants, and some cholesterol-lowering medicines can either increase the breakdown of vitamin D or reduce its absorption.

The Role of Sunlight: The Primary Source

One of the most significant factors influencing vitamin D levels is exposure to sunlight. The body synthesizes vitamin D3 when ultraviolet B (UVB) radiation from the sun hits the skin. The effectiveness of this process can be reduced by factors like geographic location, season, time of day, skin pigmentation, and the use of sunscreen and clothing.

Dietary Intake and Absorption Issues

Inadequate dietary intake and problems with absorption are significant contributors to deficiency. Few foods naturally contain substantial amounts of vitamin D. While fortified foods exist, relying solely on diet may be insufficient, especially with limited sun exposure. Additionally, certain gastrointestinal and medical conditions, such as inflammatory bowel diseases, cystic fibrosis, and weight-loss surgery, can hinder the absorption of fat-soluble vitamin D.

Chronic Illness and Metabolic Dysfunction

Chronic health conditions, including liver and kidney disease, can affect how the body metabolizes and uses vitamin D by interfering with its conversion to an active form. Obesity is also linked to lower circulating vitamin D, as it can be stored in fat tissue.

Medication Interference

Some medications, including certain anticonvulsants, corticosteroids, and cholesterol-lowering drugs, can disrupt vitamin D metabolism or absorption.

High-Risk Populations and Lifestyle Factors

Specific groups are at increased risk. Older adults may have reduced skin synthesis and kidney function, combined with less time outdoors. Breastfed infants are at risk because human milk is low in vitamin D. Homebound individuals also face limited sun exposure.

Comparison of Key Risk Factors


Risk Factor Category	Mechanism of Action	Affected Populations	Preventative Measures
Sunlight Exposure	Reduced UVB radiation reaches skin for synthesis.	Those at high latitudes, people with darker skin, elderly, indoor workers, individuals who cover up.	Moderate sun exposure, especially in summer months; considering year-round supplementation if exposure is limited.
Dietary Intake	Insufficient consumption of vitamin D-rich or fortified foods.	Vegans, those with limited access to fortified products.	Consuming fatty fish, eggs, and fortified foods; using supplements if diet is insufficient.
Malabsorption	Conditions damage intestines or disrupt fat absorption.	Individuals with Crohn's, celiac, cystic fibrosis, or post-bariatric surgery.	Requires medical management and often high-dose supplementation under supervision.
Chronic Illness	Impaired liver or kidney function, or metabolic issues.	Patients with chronic liver or kidney disease, obese individuals.	Management of underlying disease and higher supplementation dosages may be necessary.
Medications	Drugs increase vitamin D breakdown or interfere with absorption.	Patients taking certain anticonvulsants, steroids, or cholesterol drugs.	Regular monitoring of vitamin D levels and adjustment of dosage as per a healthcare provider's recommendation.

Conclusion

Vitamin D deficiency is influenced by multiple factors, including insufficient sun exposure, dietary intake, metabolic disorders, medications, age, and lifestyle. Addressing all potential factors is key to effective management. Healthcare providers can offer personalized advice, including dietary adjustments, moderate sun exposure, and supplementation.

Frequently Asked Questions

While living in a sunny climate helps, it doesn't guarantee you won't be deficient. Factors like spending most of your time indoors, using sunscreen consistently, or having darker skin pigmentation can still limit your body's ability to produce sufficient vitamin D from sunlight.

Older adults are at higher risk because their skin becomes less efficient at producing vitamin D from sun exposure as they age. They also tend to spend less time outdoors and their kidneys are less able to convert vitamin D to its active form.

Individuals with darker skin tones should consider year-round supplementation, especially those living at higher latitudes. The increased melanin in dark skin significantly reduces the efficiency of vitamin D production from sunlight, making dietary or supplemental sources essential.

Fat cells in obese individuals can sequester vitamin D, preventing it from being released into the bloodstream for the body to use. This trapping effect means that people with obesity may need higher doses of supplementation to achieve adequate circulating levels.

Breast milk is not a rich source of vitamin D, so exclusively breastfed infants are at risk for deficiency. For this reason, pediatricians often recommend a daily vitamin D supplement for breastfed babies.

Malabsorption of vitamin D can be caused by conditions such as celiac disease, Crohn's disease, cystic fibrosis, and gastric bypass surgery. These affect the gut's ability to absorb fat-soluble vitamins, requiring specialized management.

Certain medications, including corticosteroids, some anticonvulsants (like phenobarbital), and bile acid sequestrants used for cholesterol, can either increase the breakdown of vitamin D or reduce its absorption.