What are the factors that contribute to low vitamin D?

January 4, 2026 •

4 min read

Globally, a significant portion of the population suffers from vitamin D deficiency, a condition that can arise from a complex interplay of lifestyle, medical, and environmental factors. Understanding these contributing elements is the first step toward effective prevention and management.

Quick Summary

Low vitamin D is caused by insufficient sun exposure, dietary gaps, certain health conditions like malabsorption, and specific medications impacting its synthesis and absorption.

Key Points

Sunlight is primary but variable: Your body produces most vitamin D from UVB sun exposure, but this is affected by latitude, season, time of day, and cloud cover.
Skin pigmentation matters: Higher melanin levels in darker skin reduce the efficiency of vitamin D synthesis from sunlight.
Malabsorption prevents uptake: Conditions like celiac, Crohn's, and cystic fibrosis hinder the absorption of fat-soluble vitamins, including D.
Age affects production: The skin's ability to synthesize vitamin D declines with age, increasing the risk for older adults.
Medical conditions intervene: Liver and kidney diseases impair the conversion of vitamin D to its active form, while obesity can sequester the vitamin in fat cells.
Certain medications interfere: Some drugs, including anticonvulsants and corticosteroids, can accelerate the breakdown or inhibit the absorption of vitamin D.

Introduction to Vitamin D

Vitamin D is a fat-soluble nutrient that is vital for bone health, immune function, and overall well-being. Its primary role involves regulating the absorption of calcium and phosphorus, which are crucial for maintaining strong bones. A deficiency can lead to significant health problems, including osteomalacia in adults and rickets in children. While sunshine is often cited as the main source, a variety of other factors contribute to an individual's vitamin D status. Addressing low levels requires understanding the complex factors involved, which can vary widely depending on a person's lifestyle, health, and geographic location.

Environmental and Lifestyle Factors

Environmental and lifestyle choices are among the most common reasons for inadequate vitamin D levels.

Lack of Adequate Sun Exposure

The body primarily produces vitamin D through sun exposure, but this is influenced by several factors:

Geographic location: Living at higher latitudes means less access to the necessary UVB radiation, particularly in winter.
Indoor lifestyle: Spending significant time indoors reduces skin exposure to sunlight.
Seasonal changes: UVB intensity varies by season, with reduced synthesis in winter in many areas.
Air pollution: Pollutants can block UVB rays.
Sunscreen use: Sunscreen, while essential for skin protection, blocks the UVB rays needed for vitamin D synthesis.
Clothing: Covering the skin limits the area for sun exposure.

Skin Pigmentation

Melanin, which gives skin its color, acts as a natural sunscreen. Individuals with darker skin have more melanin, which absorbs more UVB radiation and thus reduces their ability to produce vitamin D from sunlight. They often need more sun exposure than those with lighter skin to synthesize the same amount of vitamin D.

Aging

With age, the skin's capacity to produce vitamin D from sunlight diminishes. Older adults may also spend less time outdoors and consume less vitamin D in their diet, increasing their risk of deficiency.

Dietary and Absorption Issues

Dietary intake is important for vitamin D, especially when sun exposure is limited, though few foods naturally contain high amounts.

Insufficient Dietary Intake

Getting enough vitamin D from food alone can be challenging. Sources include:

Natural sources: Fatty fish (salmon, mackerel, tuna), egg yolks, beef liver, and some UV-exposed mushrooms.
Fortified foods: Products like milk, cereals, orange juice, and some plant-based milk alternatives are often fortified with vitamin D.

Malabsorption Syndromes

As vitamin D is fat-soluble, conditions affecting fat absorption can significantly impact its levels. These include celiac disease, Crohn's disease, cystic fibrosis, and gastric bypass surgery.

Medical Conditions and Medications

Certain health issues and medications can interfere with vitamin D metabolism and absorption.

Liver and Kidney Disorders

The liver and kidneys convert vitamin D into its active form. Chronic conditions like liver disease or kidney failure can impair this process, leading to deficiency.

Obesity

Individuals with obesity (BMI of 30 or more) often have lower vitamin D levels because excess fat can store the vitamin, making it less available in the bloodstream. They may require higher supplement doses to reach healthy levels.

Medications

Several medications can affect vitamin D levels:

Anticonvulsants: Drugs like phenytoin and phenobarbital can increase vitamin D breakdown.
Corticosteroids: Such as prednisone, can impact calcium absorption and vitamin D metabolism.
Bile acid sequestrants: Like cholestyramine, can bind to vitamin D in the gut, reducing absorption.
Orlistat: A weight-loss drug that inhibits fat-soluble vitamin absorption.

Comparison of Vitamin D Sources


Feature	Sunlight (UVB Exposure)	Dietary Sources (Natural)	Dietary Sources (Fortified)
Availability	Dependent on latitude, season, time of day, and weather.	Limited to a few food types, variable concentration.	Widely available in many common food products.
Type of Vitamin D	Produces Vitamin D3 in the skin.	Primarily Vitamin D3 in animal products, Vitamin D2 in some mushrooms.	Both Vitamin D2 and D3 are used for fortification.
Risk of Toxicity	Excess production is naturally regulated by the body; virtually no risk.	Negligible risk from natural intake alone.	Possible from excessive intake of supplements and fortified foods.
Best For	Efficient synthesis in moderate amounts during peak hours.	Supporting overall intake, especially for those with sun exposure limitations.	Supplementing intake for those with low levels or restrictive diets.

Conclusion

Low vitamin D levels result from various factors, including environmental elements like geography and pollution, personal characteristics like skin color and age, and medical conditions or medications. Addressing deficiency requires a comprehensive understanding of these influences. Consulting a healthcare provider for personalized guidance on sun exposure, diet, and supplementation is crucial for maintaining healthy vitamin D levels and supporting bone and immune health. For further reading, authoritative sources like the Office of Dietary Supplements at the National Institutes of Health are recommended.

Frequently Asked Questions

It is very difficult to meet daily vitamin D needs from diet alone, as few foods are naturally rich in it. While fortified foods and supplements help, sun exposure is typically the most efficient source for most people.

Yes, darker skin contains more melanin, which acts as a natural sunblock. This means individuals with darker skin require significantly more sun exposure to produce the same amount of vitamin D as those with lighter skin.

With age, the skin becomes less efficient at producing vitamin D from sunlight. Older adults also tend to spend more time indoors and may have a reduced dietary intake, increasing their risk of deficiency.

Medical conditions like celiac disease, Crohn's disease, cystic fibrosis, and kidney or liver diseases can all cause vitamin D deficiency. These conditions either hinder absorption or interfere with the body's process of converting vitamin D to its active form.

Yes, obesity is associated with lower vitamin D levels because the vitamin can become trapped in fat cells, making it less available for use by the body. Individuals with a higher BMI may need more vitamin D to maintain adequate levels.

Yes, certain medications can lower vitamin D levels. Examples include anticonvulsants, corticosteroids, and some cholesterol-lowering drugs, which can either increase its breakdown or interfere with its absorption.

In many regions, especially at higher latitudes, it is not possible to produce vitamin D from the sun during the winter months due to the low angle and reduced intensity of UVB rays. Diet and supplements are often necessary during this time.