What Happens If Your Vitamin D Levels Drop Too Low?

December 6, 2025 •

5 min read

According to the National Institutes of Health, almost one in four U.S. adults have vitamin D levels considered too low or inadequate for overall health. When your vitamin D levels drop too low, it can trigger a cascade of negative health consequences affecting your bones, immune system, and mood. This vital nutrient, sometimes called the 'sunshine vitamin,' plays a crucial role far beyond just bone health.

Quick Summary

Low vitamin D levels can lead to bone disorders like osteoporosis and rickets, causing bone pain, fractures, and muscle weakness. It may also compromise immune function, increase infection susceptibility, and impact mental health, contributing to fatigue and depression. The condition is common but can be effectively managed with supplements and lifestyle changes.

Key Points

Causes Severe Bone Disorders: Chronically low vitamin D can cause rickets in children and osteomalacia in adults, leading to soft, weak, and painful bones, as well as an increased risk of osteoporosis and fractures.
Compromises Immune Function: A weakened immune system is a consequence of vitamin D deficiency, leaving the body more vulnerable to infections and potentially contributing to autoimmune diseases.
Leads to Fatigue and Muscle Weakness: Vague but persistent symptoms like fatigue, muscle aches, and muscle weakness are common signs of insufficient vitamin D.
Increases Risk of Chronic Diseases: Low vitamin D levels have been associated with an increased risk of developing heart disease, type 2 diabetes, and certain cancers.
Impacts Mental Health: Links have been found between low vitamin D and mood changes, particularly depression.
Can Cause Hair Loss and Slow Healing: Impaired wound healing and hair loss, including conditions like alopecia areata, can also be symptoms of a deficiency.

The Core Role of Vitamin D

Vitamin D is a fat-soluble vitamin that the body produces upon exposure to sunlight, and it can also be obtained from certain foods and supplements. Its most famous role is aiding in the body's absorption of calcium and phosphorus, two minerals vital for building and maintaining strong bones. When your body doesn't get enough vitamin D, it cannot absorb calcium efficiently, forcing it to pull calcium from your skeletal system to maintain blood calcium levels, which can have devastating long-term effects on bone density and strength.

Beyond bone health, vitamin D is also involved in modulating cell growth, neuromuscular and immune function, and reducing inflammation. Research has also linked insufficient vitamin D to an increased risk for a range of chronic conditions, including heart disease, some cancers, and autoimmune diseases. While not all these associations are definitively proven to be causal, the evidence suggests a broad influence on overall wellness.

The Immediate and Long-Term Consequences of Low Vitamin D

What happens if your vitamin D levels drop too low can manifest in both subtle and severe ways. Many people with a deficiency may not experience noticeable symptoms, or they may only feel generalized aches, pains, or fatigue. However, if left unaddressed, the consequences can become much more serious over time, affecting multiple systems throughout the body.

Skeletal Consequences

Rickets in children: In children, a severe vitamin D deficiency leads to rickets, a condition causing the bones to become soft and weak. Symptoms include bowed legs, delayed motor skills, and an increased risk of fractures. While rare in developed countries today due to fortified foods, it is still a risk for infants who are exclusively breastfed and not supplemented.
Osteomalacia in adults: In adults, the equivalent condition is osteomalacia, which causes a defect in bone mineralization. This can result in chronic, throbbing bone pain (often misdiagnosed as other conditions), muscle weakness, and a higher risk of fractures.
Osteoporosis: Long-term, inadequate vitamin D is a major risk factor for osteoporosis, where bones become thin, weak, and brittle. This significantly increases the risk of bone fractures, especially in older adults.

Non-Skeletal Symptoms and Complications

Muscle weakness and pain: Vitamin D receptors are found in skeletal muscle, and a deficiency can lead to proximal muscle weakness and generalized muscle aches or cramps. This weakness can also increase the risk of falls, particularly in the elderly.
Fatigue and depressed mood: Unexplained fatigue, tiredness, and mood changes are common but non-specific symptoms of low vitamin D. Studies have found a link between low vitamin D levels and an increased risk of depression, although supplementation doesn't always show a benefit for mood.
Weakened immune system: A deficiency can compromise the immune system, making individuals more susceptible to infections. Vitamin D modulates immune function, and low levels have been associated with increased infection rates and autoimmune disorders.
Hair loss: Some research has connected low vitamin D to hair loss, particularly in cases of alopecia areata. Correcting the deficiency may help, but additional treatment is often needed.
Slow wound healing: The vitamin's role in the immune system and reducing inflammation means that a deficiency can impair the body's ability to heal wounds efficiently.

Deficiency Levels: Inadequate vs. Deficient

It's important to understand the different levels of vitamin D status, which are typically measured in a blood test of 25-hydroxyvitamin D (25[OH]D). While optimal levels are debated, a general consensus exists for categorizing status.


Health Status	Serum 25(OH)D Level (ng/mL)	Description
Deficient	<12	Associated with skeletal consequences like rickets and osteomalacia.
Inadequate	12 to <20	Insufficient for bone and overall health, potentially leading to chronic issues.
Adequate	≥20	Considered sufficient for bone and general health for most people.
Excessive	>50	Linked to potential adverse effects; toxicity risk increases at >60 ng/mL.

How to Address Low Vitamin D Levels

Supplementation: For those with a true deficiency, supplements are often the most effective treatment. A doctor may prescribe high-dose vitamin D2 (ergocalciferol) for several weeks, followed by a lower maintenance dose of vitamin D3 (cholecalciferol), which the body absorbs more easily.
Sunlight Exposure: Sensible sun exposure can help your body produce its own vitamin D. However, this method is influenced by location, skin tone, and the use of sunscreen, so it is not a reliable source for everyone year-round.
Dietary Changes: While few foods naturally contain significant vitamin D, incorporating foods like fatty fish (salmon, tuna), egg yolks, and fortified cereals, milk, and juices can help. This is typically not enough to correct a significant deficiency but can help with maintenance.

The Role of Magnesium in Vitamin D Metabolism

An often-overlooked aspect of vitamin D health is its relationship with other nutrients. Specifically, magnesium is an essential cofactor for the body to activate and utilize vitamin D. Without sufficient magnesium, vitamin D supplementation may be less effective. Patients with severe vitamin D deficiency should consider having their magnesium levels checked as well. Discussing this with a healthcare provider can provide a more comprehensive approach to treatment.

Conclusion

While many people with low vitamin D levels may experience no immediate symptoms, the long-term health risks are significant and wide-ranging. From serious bone conditions like rickets and osteoporosis to systemic issues affecting muscle function, immunity, and mental health, the consequences of a sustained deficiency should not be ignored. The good news is that with a proper diagnosis, this condition is preventable and treatable through controlled supplementation, mindful dietary choices, and lifestyle adjustments. Consulting a healthcare professional is the best way to determine your individual vitamin D status and the right course of action for your health.

A Deeper Look at Health Consequences

For those interested in the underlying research, additional information on the systemic impact of vitamin D deficiency is available. The National Center for Biotechnology Information (NCBI) has published numerous studies documenting the link between low vitamin D levels and increased risk for a multitude of chronic diseases beyond bone health. This body of evidence continues to evolve, underscoring the importance of maintaining adequate levels for long-term health and well-being. A good starting point for further reading on the broader implications can be found on their website: https://www.ncbi.nlm.nih.gov/books/NBK532266/.

Frequently Asked Questions

The initial signs of low vitamin D are often subtle and non-specific, making them easy to miss. These can include generalized fatigue, bone pain, muscle aches, and mood changes like sadness or depression.

A vitamin D deficiency is diagnosed with a simple blood test that measures the concentration of 25-hydroxyvitamin D (25[OH]D) in your blood. This test is typically ordered by a healthcare provider if you report symptoms or have risk factors for a deficiency.

While the body can produce vitamin D from sun exposure, it's not a reliable source for everyone. Factors like skin pigmentation, age, geographical location, and the use of sunscreen can limit production. Healthcare providers often recommend a combination of sun, diet, and supplements.

Few foods naturally contain high levels of vitamin D. The best natural sources are fatty fish like salmon, tuna, and mackerel. Fortified foods like milk, cereal, and orange juice are also important dietary sources.

Certain groups are at a higher risk, including older adults, breastfed infants, individuals with dark skin, people with conditions that limit fat absorption (like Crohn's disease), and those with limited sun exposure.

Vitamin D2 (ergocalciferol) comes from plant sources, while Vitamin D3 (cholecalciferol) comes from animal sources and is also produced in human skin. Research suggests that vitamin D3 might raise blood levels higher and for a longer duration than D2.

Treatment usually involves supplements, often in a high-dose, short-term prescription to quickly restore levels, followed by a lower maintenance dose. The exact dosage and duration depend on the deficiency's severity and individual needs.