Who is most likely to suffer from vitamin D deficiency? A detailed guide to risk factors

October 24, 2025 •

4 min read

According to one study, nearly 42% of adults in the United States have a vitamin D deficiency, with the figure being even higher in certain populations. Given its critical role in bone health and other bodily functions, understanding who is most likely to suffer from vitamin D deficiency is crucial for preventive care and overall well-being. This guide delves into the key demographic, lifestyle, and health factors that put individuals at an increased risk.

Quick Summary

Several groups face a higher risk of vitamin D deficiency, including older adults, individuals with darker skin, breastfed infants, and people with certain medical conditions or obesity. Limited sun exposure and specific medications also contribute to an elevated risk. Understanding these factors is key for preventive health.

Key Points

Older Adults: The elderly are more likely to have a deficiency due to decreased skin synthesis and reduced outdoor activity.
Darker Skin Tones: Higher melanin content reduces the skin's ability to produce vitamin D from sunlight, increasing risk for those with dark skin.
Limited Sun Exposure: Individuals who are homebound, institutionalized, or live in high-latitude areas are at high risk.
Malabsorption Issues: Conditions like celiac disease and Crohn's disease impair the absorption of fat-soluble vitamin D.
Obesity: Excess body fat can sequester vitamin D, making it unavailable for the body to use effectively.
Breastfed Infants: Exclusively breastfed infants are at risk because human milk contains low levels of vitamin D and require supplementation.
Kidney and Liver Disease: These conditions hinder the body's ability to convert vitamin D into its active form.

Understanding the 'Sunshine Vitamin'

Vitamin D is a fat-soluble vitamin essential for many of the body's processes. Its most well-known function is regulating calcium and phosphate absorption, which is critical for maintaining strong, healthy bones. Beyond bone health, it also plays a role in the immune system, muscle function, and nerve signaling. Unlike most vitamins, the body can produce its own vitamin D when the skin is exposed to ultraviolet B (UVB) rays from sunlight. However, insufficient sun exposure, dietary intake, or underlying health issues can lead to a deficiency, impacting a person's health in various ways.

Key Populations at Higher Risk

Certain groups of people are disproportionately affected by low vitamin D levels due to a combination of biological, environmental, and medical factors.

Older Adults: As people age, their skin's ability to synthesize vitamin D from sunlight decreases significantly. Older adults also tend to spend more time indoors and have a higher likelihood of experiencing inadequate dietary intake, compounding the problem.
People with Darker Skin: Higher levels of melanin, the pigment responsible for skin color, act as a natural sunscreen and reduce the skin's capacity to produce vitamin D from the sun's rays. This means individuals with darker skin tones need more sun exposure to produce the same amount of vitamin D as those with lighter skin. Research has shown significantly higher rates of deficiency among non-Hispanic Blacks and Hispanics compared to non-Hispanic Whites.
Breastfed Infants: Human breast milk contains only small amounts of vitamin D, making exclusively breastfed infants at risk of deficiency. Health organizations often recommend supplementing breastfed infants with 400 IU of vitamin D daily.
Individuals with Limited Sun Exposure: This group includes homebound individuals, those living in institutions like nursing homes, or people whose professions or lifestyle involve primarily indoor activities. Those living in northern latitudes or regions with consistently low sunlight are also at risk.
People with Medical Conditions Affecting Nutrient Absorption: Since vitamin D is fat-soluble, its absorption is tied to the gut's ability to absorb fat. Conditions that cause fat malabsorption, such as Crohn's disease, celiac disease, cystic fibrosis, and ulcerative colitis, significantly increase the risk of deficiency.
People with Obesity: Individuals with a body mass index (BMI) of 30 or higher are at a greater risk for low vitamin D levels. Body fat sequesters vitamin D, preventing it from circulating in the bloodstream. Therefore, higher doses of supplementation may be necessary for these individuals to reach and maintain adequate levels.
Individuals with Liver or Kidney Disease: These organs are essential for converting vitamin D to its active form. Chronic liver or kidney disease impairs this process, leading to a functional deficiency.
Gastric Bypass Patients: Weight-loss surgeries like gastric bypass reroute the small intestine, which is where vitamin D is absorbed. This reduces the body's capacity to absorb the vitamin, often requiring lifelong supplementation.
People Taking Certain Medications: Some medications, including corticosteroids, weight-loss drugs (like Orlistat), and certain anti-seizure drugs, can interfere with vitamin D metabolism.

Lifestyle Factors vs. Health Conditions: A Comparison


Feature	Lifestyle-Related Risk Factors	Health Condition-Related Risk Factors
Cause	Primarily due to environmental or personal choices affecting sun exposure and diet.	Stem from underlying medical issues that impede vitamin D absorption or metabolism.
Examples	Limited sun exposure due to latitude, seasonal changes, or working indoors; religious practices requiring full body coverage; consistent sunscreen use; vegan or restrictive diets.	Malabsorption disorders (Crohn's, celiac disease), chronic liver or kidney disease, obesity, gastric bypass surgery.
Solution	Primarily addressed through diet, supplements, and increasing safe sun exposure.	Often requires higher-dose supplementation under medical supervision, alongside managing the underlying condition.
Monitoring	Less complex; often a part of routine health checks.	Requires more vigilant and consistent medical monitoring to ensure levels are maintained.

How to Mitigate Risk

For those who fall into a high-risk group, several steps can be taken to prevent or treat a vitamin D deficiency:

Increase Safe Sun Exposure: Spending a moderate amount of time in the sun, particularly during the middle of the day, can help. For many, about 10–30 minutes of direct sun exposure on arms and legs a few times per week is sufficient. However, individuals with darker skin may require more time. Remember to balance sun exposure with protecting yourself from skin cancer by avoiding sunburns.
Incorporate Vitamin D-Rich Foods: While food alone is often not enough, certain foods can boost your intake. These include:
- Fatty fish (salmon, mackerel, sardines)
- Cod liver oil
- Egg yolks
- Fortified foods like milk, cereals, and some plant-based beverages
Use Supplements: For many at-risk individuals, supplementation is the most effective way to ensure adequate vitamin D intake. Dosages vary based on age, risk level, and blood levels. It's crucial to consult a healthcare provider to determine the right dose.
Regular Monitoring: Especially for those with underlying health conditions, regular blood tests can help a doctor monitor vitamin D levels and adjust treatment plans accordingly.

Conclusion

Vitamin D deficiency is a widespread issue, but the risks are not evenly distributed across the population. While age, skin pigmentation, and limited sun exposure are common culprits, underlying health problems like malabsorption disorders, liver and kidney disease, and obesity significantly heighten the risk for certain individuals. By understanding the specific risk factors that apply to them, individuals can work with healthcare providers to develop a personalized strategy for prevention and management, including dietary changes, targeted supplementation, and lifestyle adjustments. Awareness is the first and most important step toward maintaining optimal vitamin D levels and safeguarding long-term health.

Authoritative Source

For additional medical information on vitamin D, please visit the National Institutes of Health's Office of Dietary Supplements website: Vitamin D Fact Sheet for Health Professionals.

Frequently Asked Questions

The primary way our body synthesizes vitamin D is through sun exposure. When UVB rays from sunlight hit the skin, it triggers the conversion of a compound into vitamin D3.

Older adults are at higher risk because their skin's efficiency at producing vitamin D decreases with age, and they tend to have less sun exposure and potentially lower dietary intake.

People with darker skin have more melanin, which acts as a natural sunscreen. This reduces the amount of UVB radiation that penetrates the skin, requiring them to have longer sun exposure to produce the same amount of vitamin D as those with lighter skin.

Yes, conditions that cause fat malabsorption, such as celiac disease and Crohn's disease, can lead to a deficiency. Chronic kidney or liver disease can also interfere with the body's ability to metabolize vitamin D.

Obese individuals have lower vitamin D levels because body fat sequesters the fat-soluble vitamin, preventing it from circulating freely in the bloodstream. This means more of the vitamin is stored rather than being available for the body to use.

Yes, because human breast milk contains only small amounts of vitamin D. Health organizations recommend that exclusively breastfed infants receive a daily vitamin D supplement.

The best dietary sources include fatty fish like salmon and mackerel, cod liver oil, and egg yolks. Fortified foods such as milk, certain cereals, and some plant-based milks are also good sources.

Yes, some medications can interfere with vitamin D metabolism. Examples include corticosteroids, certain weight-loss drugs, and some anti-seizure medications.