What can cause vitamin D deficiency? Understanding the key factors

October 7, 2025 •

5 min read

According to research, a significant portion of the global population is affected by low vitamin D levels. This widespread issue raises a crucial question: what can cause vitamin D deficiency? Understanding the primary drivers, including lack of sunlight, dietary inadequacies, and underlying health problems, is key to both prevention and management.

Quick Summary

Vitamin D deficiency results from insufficient sun exposure, inadequate intake from diet or supplements, and poor absorption due to certain health conditions. Key risk factors include age, darker skin, obesity, medications, and kidney or liver disease.

Key Points

Limited Sunlight: Insufficient exposure to sunlight is the leading cause of vitamin D deficiency for many people globally.
Dietary Intake: Low consumption of foods naturally rich in vitamin D or fortified products can contribute to low levels.
Malabsorption Issues: Conditions like Crohn's, Celiac disease, and cystic fibrosis can prevent the proper absorption of vitamin D.
Skin Pigmentation: Individuals with darker skin tones have higher melanin, which reduces the skin's capacity to produce vitamin D from sunlight.
Obesity and Age: Excess body fat can sequester the vitamin, while the skin's ability to produce it declines with age, increasing deficiency risk.
Medical Conditions: Kidney and liver diseases impair the conversion of vitamin D into its active form, disrupting its metabolism.
Medication Interference: Certain medications, including steroids and anti-seizure drugs, can increase the breakdown or block the absorption of vitamin D.
Environmental Factors: Air pollution can block UVB rays, while living at higher latitudes limits sun exposure, both contributing to deficiency.

The Importance of Vitamin D

Vitamin D, often called the 'sunshine vitamin,' is a fat-soluble nutrient that plays a critical role in human health. Its primary function is to help the body absorb and regulate calcium and phosphate, which are essential for strong bones, teeth, and muscles. Beyond skeletal health, vitamin D also supports the immune system, nervous system, and modulates cell growth. When the body does not have enough vitamin D, it can lead to health problems like rickets in children and osteomalacia in adults, both of which cause soft and weak bones.

Primary Causes of Vitamin D Deficiency

For most people, the main source of vitamin D is exposure to sunlight. The body produces vitamin D when ultraviolet-B (UVB) rays from the sun hit the skin and convert a form of cholesterol into vitamin D3. However, many factors can disrupt this process and lead to a deficiency.

Inadequate Sun Exposure

Lack of sufficient sun exposure is the most common cause of vitamin D deficiency worldwide. This can be due to various reasons:

Geographic Location: People who live at higher latitudes, further away from the equator, receive less intense UVB radiation, especially during the winter months.
Lifestyle: Individuals who spend most of their time indoors, such as office workers, the elderly in care facilities, or those with limited mobility, miss out on this crucial vitamin-producing sunlight.
Protective Measures: The consistent use of sunscreen with an SPF of 8 or higher significantly blocks UVB rays, reducing vitamin D production. In addition, wearing clothing that covers most of the skin for religious or cultural reasons can also prevent sun exposure.
Air Pollution: Living in densely polluted cities can block UVB rays from reaching the ground, impacting vitamin D synthesis.

Poor Dietary Intake

Few foods naturally contain high amounts of vitamin D, making it challenging to meet daily requirements through diet alone. This is a particular concern for individuals who follow specific dietary patterns, such as vegans, as many vitamin D-rich sources are animal-based.

Foods that provide some vitamin D include:

Fatty fish (salmon, tuna, mackerel)
Cod liver oil
Beef liver
Egg yolks
Certain mushrooms, especially those exposed to UV light
Fortified foods, such as milk, certain cereals, and orange juice, which have vitamin D added to them.

Medical Conditions Affecting Vitamin D Levels

Even with adequate sun exposure and a vitamin D-rich diet, certain health issues can interfere with the body's ability to absorb and metabolize the vitamin effectively.

Malabsorption Syndromes

These conditions compromise the intestines' ability to absorb nutrients, including fat-soluble vitamins like D. Examples include:

Celiac Disease: An autoimmune disorder where consuming gluten damages the small intestine lining.
Crohn's Disease: A type of inflammatory bowel disease that can affect any part of the digestive tract.
Cystic Fibrosis: A genetic disorder causing thick, sticky mucus to block ducts in the body, including the pancreas, hindering fat absorption.
Gastric Bypass Surgery: This type of weight-loss surgery alters the digestive tract, making it difficult to absorb nutrients properly.

Kidney and Liver Disease

The liver and kidneys are crucial for converting vitamin D into its active form that the body can use.

Liver Disease: Conditions like cirrhosis can lead to defective 25-hydroxylation, a vital step in activating vitamin D.
Kidney Disease: Advanced kidney disease reduces the enzyme needed for the final conversion step, resulting in a shortage of active vitamin D.

Obesity

Individuals with a body mass index (BMI) of 30 or more are at higher risk for vitamin D deficiency. This isn't because they produce less vitamin D, but because larger amounts of subcutaneous fat trap the vitamin, preventing it from circulating freely in the bloodstream. This often requires higher doses of supplementation to achieve healthy levels.

Other Significant Risk Factors

Several other factors can influence an individual's vitamin D status.

Age

As people age, their skin's ability to synthesize vitamin D from sunlight decreases. In addition, older adults tend to spend more time indoors, further increasing their risk.

Skin Pigmentation

Melanin, the pigment that gives skin its color, acts as a natural sunscreen. People with darker skin have more melanin, which significantly reduces the skin's capacity to produce vitamin D from sunlight. As a result, they are at a much higher risk of deficiency compared to individuals with lighter skin tones.

Medications

Some medications can interfere with vitamin D absorption and metabolism. Examples include:

Steroids: These can increase the breakdown of vitamin D.
Cholesterol-Lowering Drugs: Certain medications like cholestyramine can bind to vitamin D in the gut, hindering absorption.
Anti-Seizure Medications: Drugs like phenobarbital and phenytoin can increase the breakdown of vitamin D.
Weight-Loss Drugs: Orlistat, which reduces fat absorption, also reduces the absorption of fat-soluble vitamins like vitamin D.

Comparison of Key Risk Factors


Risk Factor	Mechanism	Impact on Vitamin D
Limited Sun Exposure	Reduced UVB radiation reaching the skin.	Decreased natural synthesis.
Dark Skin Pigmentation	Melanin acts as a natural sunscreen.	Less efficient vitamin D synthesis from sunlight.
Obesity	Excess fat tissue sequesters vitamin D.	Reduced bioavailability and lower circulating levels.
Malabsorption	Intestinal diseases impair fat absorption.	Inefficient absorption of dietary vitamin D.
Aging	Skin's synthesis efficiency declines with age.	Lower production of vitamin D from sun exposure.
Chronic Kidney/Liver Disease	Impairs conversion to the active form.	Body cannot use stored vitamin D effectively.
Certain Medications	Increases breakdown or blocks absorption.	Reduced levels or less effective utilization.

Conclusion

Vitamin D deficiency is a multifaceted problem with a wide range of potential causes, from simple lifestyle factors to complex medical conditions. While lack of sun exposure is a primary culprit, dietary habits, skin pigmentation, age, weight, and specific diseases all contribute to an individual's risk. Awareness of these factors is the first step towards prevention. Ensuring adequate intake through fortified foods, supplements (especially for high-risk groups), and safe, moderate sun exposure can help maintain healthy vitamin D levels. If you suspect you have a deficiency, it is important to consult a healthcare provider for proper diagnosis and a personalized treatment plan. More information on health and wellness can often be found on reputable medical sites, such as the National Institutes of Health.

Frequently Asked Questions

A vitamin D deficiency is typically diagnosed through a simple blood test that measures the level of 25-hydroxyvitamin D in your blood. You should speak with a healthcare professional to determine if testing is necessary.

While many people have no symptoms, signs can include fatigue, bone and muscle pain, muscle weakness, mood changes like depression, and in severe cases, weakened bones.

The amount of sun exposure varies based on factors like time of day, season, and skin color. Many experts suggest that 5 to 30 minutes of midday sun exposure to the face, arms, legs, or back at least twice a week is sufficient.

It is very difficult for most people to get enough vitamin D from diet alone because few foods naturally contain significant amounts. Supplements and fortified foods are often necessary.

Aging reduces the skin's efficiency in producing vitamin D, while obesity can cause the vitamin to be trapped in fat cells, making it less available for use by the body.

No, it is not possible to overdose on vitamin D from sun exposure alone. The body has a built-in mechanism that regulates production and prevents toxicity.

Conditions such as celiac disease, Crohn's disease, cystic fibrosis, and liver or kidney disease can impair the body's ability to absorb or activate vitamin D properly.

Certain medications, including steroids (like prednisone), some cholesterol-lowering drugs, and anti-seizure medications, can interfere with vitamin D levels.