Understanding Nutrition Diet: Who needs vitamin D3 the most?

October 7, 2025 •

4 min read

Worldwide, vitamin D deficiency affects a significant portion of the population, with estimates varying widely by region and demographic. This essential nutrient, often called the “sunshine vitamin,” is vital for bone health and immune function, but for certain groups, dietary intake and sun exposure are not enough, raising the critical question: Who needs vitamin D3 the most?

Quick Summary

Several groups face a heightened risk of vitamin D3 deficiency, including older adults, breastfed infants, individuals with dark skin, and those with specific medical conditions. Environmental factors like limited sun exposure also play a significant role. Supplementation is often recommended for these populations to prevent related health complications, such as compromised bone health.

Key Points

Older adults have reduced synthesis: The skin's ability to produce vitamin D from sunlight decreases significantly with age, increasing the risk of osteoporosis and fractures.
Infants need supplementation consideration: Breastfed infants, in particular, should have their vitamin D needs assessed because breast milk contains very low amounts.
Dark skin reduces absorption: Higher melanin content in darker skin acts as a natural sunscreen, significantly lowering the body's ability to synthesize vitamin D from UV rays.
Absorption issues affect availability: Conditions like celiac disease, Crohn's, and gastric bypass surgery impair the absorption of this fat-soluble vitamin, potentially requiring adjustments to ensure adequate levels.
Obesity traps vitamin D: Increased body fat can sequester vitamin D, reducing the amount that circulates in the blood and potentially necessitating a tailored approach for obese individuals.
Chronic illness impacts activation: Patients with chronic kidney or liver disease cannot properly convert vitamin D to its active form, leading to deficiency.
Sun exposure is a limiting factor: Individuals with limited sun exposure due to lifestyle, location, or consistent sunscreen use are at high risk, especially during winter months.

The Importance of Vitamin D3

Vitamin D3, or cholecalciferol, is a fat-soluble vitamin crucial for regulating calcium and phosphate absorption, which is fundamental for strong, healthy bones. Beyond its well-known role in skeletal health, vitamin D3 also modulates cell growth, neuromuscular and immune function, and helps reduce inflammation. Your body produces it when your skin is exposed to sunlight, but many factors can limit this process, making diet and supplementation necessary.

Who is at risk for vitamin D3 deficiency?

While anyone can become deficient, several groups are at a higher risk of not obtaining enough vitamin D3 through sun exposure or diet alone. Identifying these high-risk populations is key to preventing health issues such as rickets in children and osteomalacia and osteoporosis in adults.

Key populations with high vitamin D3 needs

Older Adults: With age, the skin becomes less efficient at producing vitamin D from sunlight. Older individuals also tend to spend more time indoors, further limiting their sun exposure. This combination increases their risk of deficiency, contributing to decreased bone mineral density and increased risk of fractures and falls.
Breastfed Infants: Human breast milk is a poor source of vitamin D, and pediatricians advise against exposing infants to direct sunlight. Consequently, many health authorities recommend supplementation for breastfed babies to prevent severe deficiency, which can cause rickets.
Individuals with Darker Skin: Higher levels of melanin, the pigment that gives skin its color, reduce the skin's ability to produce vitamin D from sunlight. This is a major reason why people with African, African-Caribbean, or South Asian ancestry often have lower vitamin D levels and may require year-round supplementation.
Limited Sun Exposure: People who are homebound, work night shifts, or live in northern latitudes where sunlight is insufficient during winter months are at a higher risk. Consistent use of sunscreen, while important for skin cancer prevention, also significantly blocks UV-B rays, the ones needed for vitamin D production.
Medical Conditions Affecting Absorption: Certain health issues impair the body's ability to absorb dietary fat, which is necessary for absorbing fat-soluble vitamins like D3. This includes conditions such as celiac disease, Crohn's disease, cystic fibrosis, and chronic pancreatic insufficiency.
Individuals with Obesity: Adipose tissue can sequester vitamin D, preventing its release into the bloodstream. As a result, people with a body mass index (BMI) of 30 or higher typically have lower circulating vitamin D levels and may need consideration for their vitamin D needs.
Post-Gastric Bypass Surgery Patients: Gastric bypass surgery reduces the size of the stomach and bypasses part of the small intestine, the site of vitamin D absorption. This significantly increases the risk of deficiency and necessitates lifelong supplementation consideration.
Chronic Kidney or Liver Disease: These organs are vital for converting vitamin D into its active form. Compromised kidney or liver function directly impacts the body's ability to utilize the vitamin, leading to deficiencies.
Pregnant and Lactating Women: Pregnancy and breastfeeding increase the demand for vitamin D to support both the mother's health and the baby's development. Supplementation can help prevent complications such as preeclampsia, gestational diabetes, and low birth weight.

Comparison of Risk Factors for Vitamin D3 Deficiency


Risk Factor	Mechanism Leading to Deficiency	Likelihood of Requiring Supplementation Consideration	Related Health Concerns
Older Adults	Decreased skin synthesis, reduced outdoor activity	Very High	Osteoporosis, fractures, falls
Darker Skin	Higher melanin content inhibits UV absorption	High	Lower circulating vitamin D levels
Breastfed Infants	Low vitamin D content in breast milk	Generally Recommended	Rickets, hypocalcemia
Obesity	Sequestration of vitamin D in fat tissue	High	May need tailored approach for sufficiency
Limited Sun Exposure	Insufficient UV-B radiation due to location or lifestyle	High (seasonally or year-round)	Seasonal deficiency, reduced immune function
Malabsorption Issues	Impaired intestinal absorption of fat-soluble vitamins	Very High	Severe deficiency, bone disorders
Kidney/Liver Disease	Impaired conversion to active vitamin D	Very High	Mineral and bone disorders

Nutritional strategies and supplementation

For individuals in these high-risk categories, optimizing vitamin D3 levels often requires a combination of dietary adjustments and consideration of supplementation. Few foods naturally contain vitamin D3 in significant amounts, with fatty fish like salmon, tuna, and mackerel being some of the best natural sources. Many foods, such as milk, cereals, and orange juice, are fortified with vitamin D. Cod liver oil is another source.

However, food sources alone may not be enough for those at high risk. Supplements are a common and effective way to help ensure adequate intake. Consulting a healthcare provider is essential to determine individual needs.

It is important to note that maintaining appropriate vitamin D levels is key, and healthcare providers can assist in determining this. A healthcare provider can determine vitamin D levels through a simple blood test measuring 25-hydroxyvitamin D.

Conclusion

While vitamin D is essential for everyone, certain populations are far more susceptible to deficiency due to physiological, environmental, or health-related factors. Older adults, breastfed infants, individuals with darker skin, and those with conditions affecting absorption or metabolism are among those who need vitamin D3 the most. For these individuals, proactive nutritional strategies and often, targeted supplementation, are necessary to help maintain adequate levels and prevent the associated health complications like weakened bones. Regular monitoring and discussion with a healthcare provider can help determine the right approach for maintaining optimal vitamin D levels throughout life.

For more detailed information on vitamin D and its functions, refer to the NIH Office of Dietary Supplements website.

Frequently Asked Questions

The primary cause is a combination of the skin's reduced capacity to synthesize vitamin D from sunlight and a tendency to spend less time outdoors.

Greater amounts of melanin in darker skin act as a natural UV filter, which reduces the skin's ability to produce vitamin D compared to those with lighter skin.

Yes, many health authorities recommend that exclusively breastfed babies should have their vitamin D levels evaluated, as human milk contains very little of the vitamin.

Obesity is linked to lower vitamin D levels because the vitamin gets sequestered in fat tissue, preventing its release into the bloodstream. This means a tailored approach to vitamin D intake is often necessary to achieve adequate levels.

Conditions that cause fat malabsorption, such as celiac disease, Crohn's disease, cystic fibrosis, and those who have undergone gastric bypass surgery, can significantly interfere with vitamin D absorption.

It is difficult to get enough vitamin D from the sun during autumn and winter in northern latitudes because the sun's angle is too low for effective UV-B ray exposure. Dietary intake and supplementation consideration become especially important during these months.

Severe deficiency can cause rickets, a condition of soft and weak bones, in children. In adults, it can lead to osteomalacia, which causes bone pain and muscle weakness, and increases the risk of osteoporosis.