What Happens When a Person Doesn't Get Enough Vitamin D?

December 6, 2025 •

4 min read

According to the NIH, almost one in four people in the United States have vitamin D blood levels that are too low or inadequate. This common deficiency has far-reaching effects on the body, so understanding what happens when a person doesn't get enough vitamin D is crucial for maintaining overall health.

Quick Summary

This article explores the wide-ranging consequences of insufficient vitamin D, detailing how it impacts bone strength, immune function, and mental health. It also covers common risk factors, symptoms, and treatment options to help address low vitamin D levels.

Key Points

Bone Health: Chronic vitamin D deficiency weakens bones, leading to conditions like rickets in children and osteomalacia in adults.
Immune Function: Low levels can impair the immune system, making the body more vulnerable to infections.
Mental Health: Links have been found between low vitamin D and mood disorders, including depression and anxiety.
Risk Factors: Risk factors include limited sun exposure, darker skin, older age, certain medical conditions, and obesity.
Treatment: Deficiency is typically treated with supplements, which are often more effective than dietary changes alone.
Prevention: Ensuring adequate vitamin D from sun, diet, and supplements is key to preventing health complications.

The Far-Reaching Effects of Low Vitamin D

Vitamin D is a fat-soluble vitamin essential for many bodily functions, most notably the absorption of calcium and phosphate. When the body does not have adequate vitamin D, a cascade of health issues can occur, ranging from bone weakening and muscle pain to impaired immune function and mood changes.

Impact on Bone Health

The most well-documented consequence of low vitamin D is its effect on the skeletal system. Without enough vitamin D, the body cannot absorb enough calcium and phosphorus, which are the main building blocks of bone. This leads the body to pull calcium from the bones to maintain proper blood calcium levels, a process that weakens and thins the bones over time.

In children: Severe and prolonged vitamin D deficiency can cause rickets, a rare disease where the bones become soft, weak, and deformed, leading to bowed legs and incorrect growth patterns. Early treatment is vital to prevent permanent bone damage.
In adults: The equivalent condition is osteomalacia, which causes bone pain and muscle weakness. Long-term deficiency can also accelerate bone loss, increasing the risk of osteoporosis and fractures. Older adults, in particular, face a higher risk of falls and related fractures due to weakened bones and muscles.

Effects on the Immune System

Beyond bone health, vitamin D plays a critical role in immune function. It helps the body fight off invading bacteria and viruses. Studies show a link between low vitamin D levels and a higher risk of infection. A deficiency can compromise the immune system, making a person more susceptible to illness.

Links to Mental Health

Research has explored the connection between low vitamin D levels and mental health disorders. Some studies suggest a link between vitamin D deficiency and an increased risk of depression, anxiety, and cognitive decline. While clinical trials on supplementation have yielded mixed results, some evidence points to vitamin D's potential influence on mood regulation through its presence in brain tissue. Symptoms like fatigue and mood changes, which are common in those with low vitamin D, can overlap with depressive symptoms.

Other Potential Health Consequences

In addition to the primary effects on bones and immunity, a lack of sufficient vitamin D has been linked to a number of other health problems:

Cardiovascular Disease: Some studies have connected long-term deficiency with a greater risk of heart disease and high blood pressure, though more research is needed.
Type 2 Diabetes: Vitamin D helps the body regulate blood sugar levels, and low levels have been associated with a higher risk of developing type 2 diabetes.
Autoimmune Diseases: Inadequate vitamin D has been implicated as a risk factor for certain autoimmune conditions.
Weight Gain and Fatigue: Unexplained weight gain and persistent fatigue or low energy are common, non-specific symptoms of vitamin D deficiency.

Risk Factors for Vitamin D Deficiency

Several factors can increase a person's risk of not getting enough vitamin D. These include:

Limited Sun Exposure: Living in a northern climate, being housebound, or having a job that involves little outdoor time can lead to a deficiency.
Darker Skin: Higher levels of melanin reduce the skin's ability to produce vitamin D from sunlight.
Age: The skin's efficiency at producing vitamin D declines with age.
Diet: Following a strict vegan diet or not consuming enough fortified foods can be a factor.
Medical Conditions: Malabsorption disorders like celiac disease or cystic fibrosis, and liver or kidney disease can interfere with vitamin D absorption and metabolism.
Obesity: Body fat can bind to vitamin D, preventing it from circulating in the blood.

Comparison of Vitamin D Deficiency Manifestations


Feature	Children (Rickets)	Adults (Osteomalacia/Osteoporosis)
Skeletal Impact	Soft, weak, and deformed bones, bowed legs.	Weak bones, bone pain, increased fracture risk.
Symptoms	Late walking, muscle weakness, bone pain, joint deformities.	Fatigue, bone pain, muscle aches, mood changes.
Severity	Severe cases can lead to long-term bone damage, seizures, or heart damage.	Chronic deficiency exacerbates osteoporosis and fracture risk.
Prevention/Treatment	Supplements for breastfed infants, fortified milk.	Supplements, dietary changes, and sunlight exposure.

Conclusion: The Importance of Monitoring Vitamin D Levels

Vitamin D is a critical nutrient with a profound impact on nearly every system in the body, from the strength of your bones to the health of your immune system and your mental well-being. The symptoms of deficiency can often be subtle and go unnoticed, making it important for at-risk individuals to be aware of the signs and consult a healthcare provider. Through proper sun exposure, dietary choices, and supplementation when necessary, individuals can maintain adequate levels and avoid the serious long-term consequences of a vitamin D deficit. Monitoring your vitamin D status can be a simple yet powerful step toward preserving your overall health. For more information, visit the National Institutes of Health Office of Dietary Supplements.

Frequently Asked Questions

Early or mild vitamin D deficiency often presents with subtle, non-specific symptoms such as fatigue, generalized muscle aches, bone pain, and mood changes like depression.

The body can produce vitamin D through sun exposure. Other sources include eating fatty fish like salmon and tuna, fortified milk and cereals, and taking dietary supplements.

People with limited sun exposure, older adults, those with darker skin, individuals with conditions affecting fat absorption, and people with obesity are at higher risk.

Studies have found an association between low blood levels of vitamin D and an increased risk of depression. While not all research is conclusive, vitamin D is involved in brain function, and deficiency symptoms like fatigue can overlap with mood disorders.

Vitamin D is essential for the body to absorb calcium and phosphorus, which are vital for building and maintaining strong bones. Without enough vitamin D, bones can become soft, weak, and susceptible to fractures.

Yes, excessive intake of vitamin D, almost always from supplements, can be harmful. High levels can cause nausea, vomiting, weakness, and potentially more severe issues like kidney stones and irregular heartbeats.

Rickets is a bone-softening disease caused by vitamin D deficiency that affects children during their period of bone growth. Osteomalacia is the equivalent condition in adults, causing soft bones and muscle weakness.