Who is most likely to be low in vitamin D?

December 7, 2025 •

4 min read

Worldwide, a high percentage of the population is at risk for vitamin D inadequacy, with some studies estimating this number to be as high as 50%. This makes identifying who is most likely to be low in vitamin D crucial for preventing associated health problems, from bone issues to weakened immunity.

Quick Summary

Several demographic and lifestyle factors increase the risk of vitamin D deficiency, including advanced age, darker skin pigmentation, and limited sun exposure. Certain medical conditions, obesity, and dietary habits also play a significant role in determining an individual's vitamin D status. Addressing these risk factors is vital for overall health.

Key Points

Older Adults: The skin's ability to produce vitamin D decreases significantly with age, making seniors, especially those institutionalized, highly susceptible to deficiency.
Dark Skin Tones: Higher melanin levels in darker skin reduce the effectiveness of sun exposure for vitamin D synthesis, increasing deficiency risk.
Limited Sun Exposure: People who live in high-latitude areas, work indoors, or cover their skin extensively are prone to low vitamin D levels.
Malabsorption Issues: Medical conditions like Crohn's, celiac disease, and cystic fibrosis can prevent the proper absorption of vitamin D.
Obesity and Gastric Bypass: Higher body fat can sequester vitamin D, while gastric bypass surgery reduces absorption, both increasing deficiency risk.
Exclusively Breastfed Infants: Breast milk is low in vitamin D, requiring supplements for infants to prevent deficiency.
Kidney and Liver Disease: These conditions impair the conversion of vitamin D to its active form, leading to lower levels.

Understanding Vitamin D: The 'Sunshine Vitamin'

Vitamin D is a fat-soluble vitamin essential for regulating calcium and phosphate levels in the body, which are vital for healthy bones, teeth, and muscles. It also plays a key role in the nervous system, immune function, and reducing inflammation. The body can synthesize vitamin D when skin is exposed to sunlight, but several factors can interfere with this process, leading to a deficiency.

Key Risk Groups for Low Vitamin D

Identifying the populations most susceptible to low vitamin D is the first step toward prevention and treatment. These risk factors often overlap, compounding an individual's likelihood of deficiency.

Older Adults

Age is a major risk factor for low vitamin D. As we get older, several physiological changes make it harder to maintain adequate vitamin D levels:

Reduced Skin Synthesis: The skin's ability to produce vitamin D from sunlight decreases significantly with age. By age 70, the capacity can be reduced by as much as 75%.
Limited Sun Exposure: Older adults, especially those who are housebound or in long-term care facilities, spend less time outdoors, limiting their exposure to UV-B radiation.
Dietary Factors: They may also have inadequate dietary intake of vitamin D-rich or fortified foods.

People with Darker Skin Tones

Melanin, the pigment responsible for darker skin, acts as a natural sunscreen. While this offers excellent protection from UV damage, it also reduces the skin's capacity to produce vitamin D from sunlight. Studies show that individuals with darker skin may require significantly more sun exposure—up to six times as much—to produce the same amount of vitamin D as a person with lighter skin. This is why populations with African, African-Caribbean, or South Asian backgrounds often have higher rates of deficiency.

Individuals with Limited Sun Exposure

Sunlight is the primary natural source of vitamin D. Therefore, anyone with limited exposure is at a higher risk of deficiency. This includes:

People who live in high-latitude regions, where UV-B radiation is weaker, especially during winter months.
Individuals who work indoors or have occupations that limit outdoor time.
Those who regularly wear clothing that covers most of their skin for religious or cultural reasons.
Consistent use of sunscreen, which blocks the UV rays necessary for synthesis, can also contribute to lower levels, although typical usage may not completely prevent production.

People with Certain Medical Conditions

Several health issues can impact the body's ability to absorb, metabolize, or use vitamin D, leading to deficiency.

Malabsorption Syndromes: Conditions that affect fat absorption, such as Crohn's disease, celiac disease, cystic fibrosis, and ulcerative colitis, can hinder the absorption of this fat-soluble vitamin.
Obesity: Individuals with a BMI of 30 or higher often have lower serum vitamin D levels because the vitamin is sequestered in fat cells, making it less available in the bloodstream.
Kidney and Liver Disease: These organs are crucial for converting vitamin D into its active form. Chronic kidney disease and liver disease, like cirrhosis, can disrupt this conversion process.

Exclusively Breastfed Infants

Breast milk contains very little vitamin D. As a result, infants who are exclusively breastfed are at a high risk of deficiency and rickets if they do not receive a vitamin D supplement. The American Academy of Pediatrics recommends that all breastfed infants receive a daily supplement of 400 IU of vitamin D.

Comparison of Risk Factors


Risk Factor Category	High-Risk Groups	Key Mechanisms Affecting Vitamin D	Prevention & Management Strategy
Age	Older adults (>65), especially institutionalized individuals	Decreased skin synthesis, less outdoor time, lower dietary intake	Daily supplementation (800-1,000 IU), dietary changes, monitored sun exposure
Skin Pigmentation	People with darker skin tones (e.g., African, South Asian descent)	Higher melanin content blocks UVB rays, reducing skin synthesis	Daily supplementation often recommended, may require higher doses
Sun Exposure	High-latitude residents, indoor workers, covered skin	Insufficient UVB exposure, either seasonally or chronically	Daily supplementation during winter, sensible sun exposure in summer
Medical Conditions	Malabsorption syndromes, obesity, kidney/liver disease	Impaired absorption, storage, or conversion of vitamin D	Targeted supplementation, often with higher doses, managed by a healthcare provider
Dietary Habits	Vegans, low intake of fortified foods	Lack of dietary sources, as many are animal-based or fortified dairy	Regular intake of fortified foods, fortified plant-based milk, or supplements

How to Prevent Vitamin D Deficiency

Prevention is often the best strategy for maintaining healthy vitamin D levels. Here are several approaches:

Safe Sun Exposure: Spend 5-30 minutes in direct sunlight, two or three times per week, with face, arms, and legs exposed. The best times are generally between 10 a.m. and 3 p.m.. However, this should be balanced with skin cancer risks, so consult a doctor about safe limits, especially for fair-skinned individuals.
Dietary Sources: Incorporate foods naturally rich in vitamin D, such as fatty fish (salmon, mackerel, sardines), fish liver oils, egg yolks, and beef liver.
Fortified Foods: Many common foods are fortified with vitamin D, including milk, orange juice, and some breakfast cereals. Check product labels for vitamin D content.
Supplements: If sun exposure or diet is insufficient, a vitamin D supplement is a reliable option. Dosages vary by age and risk factors, so it is best to consult a healthcare provider for personalized recommendations.

Conclusion

While vitamin D deficiency is a widespread issue, certain groups are disproportionately affected due to factors like age, skin pigmentation, geographic location, and medical conditions. Older adults and individuals with darker skin are at particularly high risk. Awareness of these specific risk factors is key for identifying who should be screened and monitored more closely. By combining sensible sun exposure, dietary adjustments, and strategic supplementation, many people can successfully manage their vitamin D levels and protect their skeletal and overall health. If you suspect you may be at risk, speaking with a healthcare professional can provide clarity and a tailored plan to ensure you get the vital vitamin D your body needs.

Authoritative Link: National Institutes of Health (NIH) Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals

Frequently Asked Questions

Initial symptoms can be subtle and non-specific, often including fatigue, muscle aches, bone pain (especially in the back), muscle weakness, or a general sense of unwellness. In children, delayed walking or soft skull bones (rickets) can be a sign.

It is difficult to get enough vitamin D from diet alone, as only a few foods are naturally rich in it, such as fatty fish, beef liver, and egg yolks. Fortified foods help, but for many, sunlight or supplements are necessary to reach optimal levels.

Yes, sunscreen with a Sun Protection Factor (SPF) of 8 or higher can block the UVB rays needed for vitamin D synthesis. However, most people do not apply it perfectly, so some production may still occur. Balanced, sensible sun exposure is recommended for vitamin D, followed by sun protection.

Vitamin D is a fat-soluble vitamin that gets stored in the body's fat cells. In individuals with obesity, a higher amount of this vitamin gets sequestered in their larger fat stores, making less of it available in the bloodstream.

Treatment typically involves supplementation with either vitamin D2 or D3, often at a higher dose initially to replenish stores, followed by a lower daily maintenance dose. The specific regimen should be determined by a healthcare provider based on the individual's severity of deficiency.

In rare cases, vitamin D deficiency can be hereditary, such as with hereditary vitamin D-resistant rickets. For the vast majority, however, lifestyle, diet, and underlying medical conditions are the primary drivers.

With supplementation, it generally takes about 6 to 8 weeks for vitamin D levels to return to a healthy range. However, the exact timeline depends on the severity of the deficiency and the prescribed treatment plan.