Who Is Most at Risk of Vitamin D Deficiency?

Published on March 18, 2026

11 Key Factors That Influence Your Vitamin D Levels

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Vitamin D deficiency is one of the most common nutritional deficiencies worldwide, yet it does not affect everyone equally.  While seasonal changes, especially the winter months, play a major role in lowering vitamin D levels, there are several well-established factors that can significantly increase an individual’s risk of deficiency year-round.

Last week, we focused on the influence of the seasons on vitamin D levels, and how this time of year is when a majority of the population is at their highest risk of deficiency.  Understanding the additional following risk factors for vitamin D deficiency is essential for both individuals and practitioners, as it helps identify who may need higher intake, closer monitoring, or more frequent testing year-round.

Why Risk Varies from Person to Person

Vitamin D levels are influenced by a combination of:

• Sun exposure
• Skin pigmentation
• Body composition
• Age
• Diet and supplementation
• Genetics
• Overall health status

Because of this, two people taking the same amount of vitamin D—or getting the same amount of sun—can have very different blood levels.

This variability is one of the key reasons why testing is essential.

11 Key Risk Factors for Vitamin D Deficiency

1. Limited Sun Exposure, Sun Avoidance, and Sunscreen Use

Vitamin D is produced in the skin when exposed to UVB radiation from sunlight, and for those who do not supplement, sunlight becomes a key determinant of their vitamin D status.  Individuals at higher risk include:

• Those who spend most of their time indoors
• People who live in northern latitudes
• Individuals experiencing winter months with minimal UVB availability
• Those who consistently avoid sun exposure or cover most of their skin
• Individuals who regularly use sunscreen during all sun exposure

Even in sunny regions, modern indoor lifestyles, sun avoidance, and protective behaviors can significantly limit vitamin D production.

2. Darker Skin Pigmentation

Melanin reduces the skin’s ability to produce vitamin D from sunlight.  As a result:

• Individuals with darker skin require more sun exposure to produce the same amount of vitamin D
• Risk of deficiency is significantly higher, particularly in regions with limited sunlight

3. Aging

As we age, the skin becomes less efficient at producing vitamin D.  Older adults may also:

• Spend less time outdoors
• Have reduced dietary intake
• Have an increased incidence of chronic disease
• Be on medications affecting vitamin D (see below)
• Experience decreased liver or kidney function, which affects vitamin D activation

4. Overweight and Obesity

Body fat can sequester vitamin D, reducing its availability in circulation.  Research has shown that:

• Individuals with higher body weight often require 2–3 times more vitamin D to achieve the same blood levels
• Obesity is consistently associated with lower 25(OH)D levels

5. Inadequate Supplementation or Intake

Many individuals rely on standard recommendations that may be too low to achieve optimal levels.  Most also fail to retest vitamin D levels after adjusting intake to ensure that intake is the correct dose for them.  Without sufficient intake and monitoring of serum levels:

• Vitamin D stores decline, especially during winter
• Blood levels may fall into deficient or insufficient ranges

6. Genetics and Individual Variability

Genetic differences can affect how vitamin D is:

• Absorbed
• Transported
• Activated
• Utilized at the cellular level

Some individuals may have a blunted response to supplementation, sometimes referred to as “vitamin D resistance.”

7. Gastrointestinal or Malabsorption Issues

Digestive conditions that affect fat absorption can impair vitamin D uptake.  Examples include:

• Celiac disease
• Inflammatory bowel disease (IBD)
• Bariatric surgery
• Chronic digestive disorders

Because vitamin D is fat-soluble, proper absorption is essential.

8. Pregnancy and Increased Physiological Demand

Vitamin D requirements increase during pregnancy. Without adequate intake:

• Maternal levels may decline
• Risk of maternal and infant health conditions increases
• Fetal development may be affected
• Postpartum deficiency is common

Optimizing vitamin D status during pregnancy is increasingly recognized as an important factor in maternal and infant health.

9. Chronic Health Conditions

Certain conditions are associated with lower vitamin D levels or altered metabolism. These may include:

• Kidney disease
• Liver disease
• Endocrine disorders
• Chronic inflammatory conditions

These individuals may require closer monitoring and individualized dosing.

10. Medications That Affect Vitamin D Metabolism

Certain medications can interfere with vitamin D absorption, metabolism, or activation, increasing the risk of deficiency. Common examples include:

• Glucocorticoids (steroids)
• Anticonvulsants
• Weight-loss medications that reduce fat absorption
• Cholesterol-lowering medications (such as bile acid sequestrants)

These medications may reduce circulating vitamin D levels or impair how vitamin D is utilized in the body, making monitoring and adjustment especially important for individuals taking them.

11. Inadequate Co-Nutrient Status

Vitamin D does not work in isolation and relies on several key nutrients for proper absorption, activation, and function in the body. Important co-nutrients include:

• Magnesium (required for vitamin D metabolism and activation)
• Vitamin K (supports calcium regulation and proper distribution)
• Omega-3 fatty acids (support anti-inflammatory pathways)
• B vitamins (involved in energy metabolism and cellular function)
• Zinc and boron (support immune function and vitamin D activity)

If these co-nutrients are insufficient:

• Vitamin D may not be properly activated
• The body’s response to supplementation may be reduced
• Higher doses of vitamin D may be required to achieve optimal levels

Optimizing these co-nutrients is an important but often overlooked factor in achieving and maintaining healthy vitamin D status.

Many People Have More Than One Risk Factor

It’s important to recognize that these risk factors often overlap.  For example, an individual may:

• Work indoors
• Have darker skin
• Be overweight
• Live in a northern climate

Each additional factor can further increase the likelihood of deficiency.  Measure your risk of vitamin D deficiency with our quiz here.

Why Testing Matters—Especially for High-Risk Groups

Because vitamin D status varies so widely between individuals, testing is the only way to know your level.  Testing serum 25-hydroxyvitamin D [25(OH)D] allows you to:

• Identify deficiency or insufficiency
• Understand your personal response to supplementation
• Adjust intake based on your individual needs
• Monitor changes over time

For individuals with one or more risk factors, testing becomes even more important.

Vitamin D deficiency is not just a seasonal issue—it is influenced by a wide range of personal and environmental factors.

Understanding your individual risk can help guide:

• When to test
• How much vitamin D you may need
• How to maintain healthy levels throughout the year

By combining awareness of risk factors with regular testing, individuals and practitioners can take a more personalized and effective approach to vitamin D optimization.

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Measure Your Vitamin D and Other Important Nutrients

If you haven’t had your vitamin D levels checked recently, now is the time! With so many Americans still falling short, awareness is the first step toward change.

Measuring and calculating a supplementation amount to help reach and maintain a target level, or taking loading doses to correct deficiency faster, could possibly make all the difference in overall health, wellbeing, and how a current disease situation progresses. Test your level now!

Create your custom home blood spot kit by adding any of the following measurements, along with your vitamin D:

• Omega-3 Index (with or without Ratios AA:EPA and Omega-6:Omega-3)
• Magnesium (with additional Elements copper, zinc, selenium, mercury, and cadmium)
• hsCRP as a marker of inflammation and HbA1c as a marker of blood sugar health

Having and maintaining healthy vitamin D levels and other nutrient levels can help improve your health, now and for the future. Enroll and test your levels today, learn what steps to take to improve your status of vitamin D (see below) and other nutrients and blood markers, and take action! By enrolling in the GrassrootsHealth projects, you are not only contributing valuable information to everyone, you are also gaining knowledge about how you could improve your own health through measuring and tracking your nutrient status, and educating yourself on how to improve it.