What Happens If Vitamin D Goes Too Low? Serious Health Risks Explored

November 17, 2025 •

4 min read

According to the National Institutes of Health, vitamin D deficiency is a global health concern, affecting a significant portion of the population worldwide. When vitamin D goes too low, it can lead to a cascade of health issues, impacting not just bone health but also immune function and overall well-being.

Quick Summary

A severe drop in vitamin D levels can cause serious health complications, including bone weakening, chronic pain, and a weakened immune system. It can manifest as rickets in children and osteomalacia in adults, affecting calcium absorption and overall skeletal health.

Key Points

Causes Severe Bone Disorders: When vitamin D is too low, children can develop rickets, while adults are at risk for osteomalacia and osteoporosis, which soften and weaken bones.
Triggers Secondary Hyperparathyroidism: Chronic deficiency causes the parathyroid glands to overcompensate, pulling calcium from bones to maintain blood levels, leading to accelerated bone demineralization.
Leads to Muscle Weakness and Pain: Low vitamin D is a frequent cause of unexplained muscle weakness, cramps, and aches in adults.
Weakens the Immune System: Vitamin D plays a role in immune modulation; deficiency can lead to an increased risk of infections.
Is Associated with Mood Changes: Low levels have been linked to an increased risk of depression and other mood disorders.
Raises Risk for Other Chronic Conditions: Long-term deficiency is correlated with a higher risk of cardiovascular disease, autoimmune disorders, and diabetes.
Often Correctable with Supplementation: The condition is treatable and preventable with proper supplementation, dietary changes, and moderate sun exposure, under medical supervision.

Understanding the Role of Vitamin D

Vitamin D is a fat-soluble vitamin that plays a vital role in several bodily functions, most famously its partnership with calcium and phosphorus to build and maintain strong bones. However, its functions extend far beyond the skeletal system. Vitamin D receptors are present in many tissues throughout the body, where it influences cell growth, neuromuscular function, immune response, and inflammation. Your body primarily gets vitamin D through sun exposure, and also through certain foods and supplements. A sustained lack of this crucial nutrient is known as a vitamin D deficiency.

Immediate Health Consequences

When levels of vitamin D drop, the body's ability to absorb calcium and phosphorus from the intestines is impaired. This has direct and immediate effects on bone health. In response to low blood calcium, the body increases parathyroid hormone (PTH) production, which pulls calcium from the bones to restore blood levels. This process is known as secondary hyperparathyroidism and leads to bone demineralization.

Skeletal and Muscular Symptoms

Bone Pain and Weakness: Adults may experience generalized bone pain, especially in the hips, legs, and lower back, a condition known as osteomalacia. The bones become soft and weak, making them susceptible to fractures.
Muscle Weakness and Aches: Low vitamin D can cause unexplained muscle weakness, aches, and cramps throughout the body. This is particularly notable in older adults and can increase the risk of falls.
In Children: For children, a severe vitamin D deficiency results in rickets, a condition where growing bones become soft and misshapen, leading to bowed legs and incorrect growth patterns.

Long-Term and Systemic Effects

If left unaddressed, a vitamin D deficiency can contribute to a host of long-term health issues beyond bone density loss. Research has linked low vitamin D status to an increased risk of chronic conditions, indicating its broad impact on the body.

Immune System Compromise

Vitamin D modulates the immune system and low levels are associated with increased susceptibility to infections. Studies have shown that vitamin D enhances the body's natural defenses, and a deficiency may weaken its ability to fight off viral and bacterial illnesses.

Mood and Mental Health

There is a notable association between low vitamin D and mood disorders, including depression. While more research is needed to determine the causal link, some studies have shown that supplementation can help alleviate symptoms of depression in those who are deficient.

Potential Link to Chronic Diseases

Mounting evidence suggests that low vitamin D levels may be associated with a higher risk for various chronic diseases. These include cardiovascular disease, certain types of cancer, autoimmune diseases like multiple sclerosis and rheumatoid arthritis, and impaired glucose metabolism, which can increase the risk of type 2 diabetes.

Comparison of Effects: Adults vs. Children


Symptom	Children	Adults
Primary Bone Disorder	Rickets (soft, bent bones)	Osteomalacia (soft bones)
Skeletal Deformities	Bowed legs, skeletal deformities, and dental problems	Increased risk of fractures, especially in the hips, and osteoporosis
Growth Patterns	Stunted or incorrect growth patterns, delayed walking	Bone density loss and increased fragility
Muscle Symptoms	Weak, sore, or painful muscles, possible muscle spasms	Muscle weakness, aches, and cramps
Key Concern	Proper development of the growing skeleton	Preservation of bone density and prevention of fractures

How to Prevent and Treat Low Vitamin D

Addressing low vitamin D typically involves increasing intake through dietary sources, sun exposure, and supplementation. Sunlight exposure is the most natural way to produce vitamin D, but factors like skin tone, age, and geographical location can limit this. For many, especially during winter months or for those with specific health conditions, supplementation is a critical component of treatment. Regular monitoring of serum 25-hydroxyvitamin D levels through a blood test is the standard for diagnosis. Discussing the appropriate dosage with a healthcare provider is essential, as individual needs can vary.

Conclusion

What happens if vitamin D goes too low? The consequences are far-reaching and can affect everything from the strength of your bones to the resilience of your immune system. While the more severe outcomes like rickets are rare in many developed countries, mild to moderate deficiency is widespread and can still cause significant health issues like fatigue, chronic pain, and an increased risk of more serious conditions over time. Fortunately, this condition is both preventable and treatable with a combination of healthy lifestyle habits and medical guidance. Individuals concerned about their vitamin D levels should consult a healthcare professional for testing and personalized advice.

Optional Outbound Link

For more detailed information on recommended dietary allowances for vitamin D, consult the Office of Dietary Supplements at the National Institutes of Health.

Frequently Asked Questions

Early and often subtle signs of low vitamin D can include fatigue, muscle aches or weakness, and generalized bone pain. Many people may not notice symptoms until the deficiency becomes more significant.

Yes, chronic fatigue and low energy are common symptoms associated with a vitamin D deficiency. The fatigue can be persistent and may not improve with rest, indicating an underlying nutritional issue.

A vitamin D deficiency is diagnosed with a simple blood test that measures the level of 25-hydroxyvitamin D in your blood. Your doctor can order this test if a deficiency is suspected.

For many, especially those with darker skin, older adults, and people living at higher latitudes, relying solely on sun exposure is insufficient. The use of sunscreen and spending most of your time indoors also reduces production. Dietary sources and supplements are often necessary.

Foods containing vitamin D include fatty fish like salmon, tuna, and mackerel, as well as beef liver, egg yolks, and certain fortified foods such as milk, cereals, and orange juice.

Rickets affects children whose bones are still growing, causing them to become soft, bent, or misshapen. Osteomalacia is the adult equivalent, where existing bones soften, leading to fractures and bone pain.

The time it takes to restore normal vitamin D levels depends on the severity of the deficiency and the treatment plan. With consistent supplementation under a doctor's guidance, many individuals can correct their levels over several months.