What happens if I don't take vitamin D?: Understanding the health risks

October 10, 2025 •

4 min read

According to the World Health Organization, millions worldwide suffer from vitamin D deficiency, a widespread nutritional issue. Understanding the significant health consequences is crucial for anyone wondering, what happens if I don't take vitamin D?, as the effects extend far beyond bone health.

Quick Summary

A lack of vitamin D can lead to bone weakening conditions like rickets and osteomalacia, increased risk of fractures, and muscle pain. It also compromises immune function and contributes to fatigue, low mood, and other chronic health issues.

Key Points

Bone Weakening: A lack of vitamin D hinders calcium absorption, leading to conditions like osteomalacia and osteoporosis, which increase the risk of fractures.
Muscle Dysfunction: Deficiency can cause muscle weakness, aches, and pain, increasing the risk of falls, especially in older adults.
Impaired Immunity: Low vitamin D levels can compromise the immune system, making the body more susceptible to infections like the common cold and flu.
Mood Changes: Fatigue and low mood are common symptoms, and studies have linked lower vitamin D levels with an increased risk of depression.
Increased Chronic Disease Risk: Long-term deficiency is associated with a greater risk of developing chronic conditions, including cardiovascular disease and autoimmune disorders.
Rickets in Children: Severe deficiency in children can cause rickets, a rare but serious condition that results in soft, weak, and deformed bones.

The Core Functions of Vitamin D

Often referred to as the 'sunshine vitamin,' vitamin D is a fat-soluble nutrient that plays a critical role in numerous bodily functions. Its most widely known function is facilitating the absorption of calcium and phosphate from the gut, which is essential for developing and maintaining strong bones. Without adequate vitamin D, the body cannot effectively utilize these minerals, regardless of how much is consumed through diet.

Beyond its effect on bone health, vitamin D is also vital for the proper functioning of the immune system. It helps modulate the immune response, assisting in the fight against invading bacteria and viruses. Nerve and muscle function also depend on sufficient vitamin D levels, highlighting its importance for overall movement and nervous system signaling.

Immediate Consequences of Low Vitamin D

For many, the initial signs of insufficient vitamin D are subtle and can easily be mistaken for other common ailments. Over time, however, these symptoms can worsen and significantly impact quality of life.

Symptoms in Adults

In adults, low vitamin D can manifest through several key indicators:

Chronic fatigue and low energy levels.
Generalized aches, pains, or weakness in muscles.
Bone pain, particularly in the lower back, hips, pelvis, and legs.
Mood changes, including an increased risk of depression.
Impaired wound healing.

Symptoms in Children

In children, the symptoms of severe deficiency are more pronounced and can lead to irreversible damage. Rickets, a disease where bones become soft and bent, is the most well-known consequence. Signs may include delayed walking, bone pain, and skeletal deformities like bowed legs.

Long-Term Health Risks of Deficiency

Sustained vitamin D deficiency significantly raises the risk of developing more severe and chronic health problems. The body's constant effort to maintain blood calcium levels by drawing from bone stores can lead to serious deterioration of the skeleton.

Skeletal Health Deterioration

Osteomalacia (in adults): The adult equivalent of rickets, this condition causes painful, weak, and softened bones due to impaired mineralization.
Osteoporosis (in adults): A condition characterized by thinned, brittle bones that are more susceptible to fractures. Studies link low vitamin D levels with an increased risk of fractures in older adults, especially hip fractures resulting from minor falls.

Weakened Immune Response

A properly functioning immune system relies on sufficient vitamin D. Prolonged deficiency can lead to increased susceptibility to infections and a higher risk of developing certain autoimmune diseases, such as multiple sclerosis and type 1 diabetes. It has been shown that vitamin D can temper the inflammatory response of some immune cells, so a lack of it can hinder this crucial protective mechanism.

Association with Chronic Diseases

Mounting research suggests a link between vitamin D deficiency and an elevated risk of several chronic conditions:

Cardiovascular Disease: Vitamin D plays a role in regulating heart and blood vessel health. Severe deficiency has been linked to an increased risk of heart disease and high blood pressure.
Type 2 Diabetes: Low vitamin D levels may negatively affect the regulation of blood sugar levels and contribute to insulin resistance.
Certain Cancers: Some studies have explored a possible link between low vitamin D levels and an increased risk of certain cancers, though the evidence remains mixed and requires more research.

How to Avoid Vitamin D Deficiency

Preventing vitamin D deficiency is typically straightforward and involves a combination of sun exposure, dietary intake, and potentially supplements. People at higher risk, such as older adults, those with dark skin, and individuals with certain medical conditions, may need special attention.

Comparison of Vitamin D Intake Methods


Method	Pros	Cons	Notes
Sunlight	Natural, free, and efficient way to produce vitamin D.	Sun exposure risk (skin cancer), variable production (latitude, season, time of day), and limited in many locations.	A few minutes of daily sun exposure (10-4 p.m.) is often sufficient, but varies by skin tone and location.
Dietary Sources	Safe and natural way to get vitamin D through food.	Very few foods naturally contain high amounts of vitamin D. Fortified foods provide some, but may not be enough.	Good sources include fatty fish (salmon, trout), eggs, beef liver, and UV-exposed mushrooms. Fortified foods include milk and cereal.
Supplements	Convenient, consistent dosage, and effective for those with limited sun exposure or dietary intake.	Overconsumption can lead to toxicity (hypercalcemia), potential interactions with medications, and unregulated quality in some areas.	Recommended for many during winter months or for those with risk factors. Should consult a doctor for appropriate dosage.

Conclusion

Ignoring the need for vitamin D can have profound and lasting health consequences, from the softening of bones in childhood (rickets) and adulthood (osteomalacia) to compromised immune function and increased risk of fractures and chronic diseases. Fortunately, maintaining sufficient vitamin D is achievable through a balanced approach incorporating safe sun exposure, rich dietary sources like fatty fish, and fortified foods. For many, particularly during winter or with pre-existing conditions, supplements provide a reliable path to prevention. Proactive management of vitamin D levels is a simple yet powerful step toward long-term health and well-being. For a deeper dive into the science, refer to the National Institutes of Health Fact Sheet on Vitamin D.

Frequently Asked Questions

The initial signs of a vitamin D deficiency are often subtle and can include fatigue, bone pain, muscle aches, and changes in mood, such as depression. Many people with mild deficiency may not even notice symptoms.

Yes, vitamin D is necessary for proper brain function and mood regulation. Some studies have found a link between low blood levels of vitamin D and an increased risk of depression, though research on supplementation for treatment shows mixed results.

While vitamin D is crucial for bone health and mineral absorption, its deficiency also impacts muscle strength, immune system function, and potentially increases the risk for chronic diseases like cardiovascular disease and type 2 diabetes.

Rickets is a bone disorder caused by severe vitamin D deficiency in children, where growing bones become soft and deformed. Osteomalacia is the adult equivalent, where existing bones soften and weaken due to defective mineralization.

If sun exposure is limited, you can increase your intake through diet and fortified foods. Excellent food sources include fatty fish (salmon, mackerel), egg yolks, and fortified products like milk and cereal. Supplements are also a reliable option.

Yes, several groups are at higher risk, including older adults (whose skin is less efficient at producing vitamin D), people with darker skin, breastfed infants, individuals with limited sun exposure, and people with conditions that impair fat absorption.

A vitamin D deficiency is diagnosed through a blood test that measures serum 25-hydroxyvitamin D levels. Treatment typically involves taking supplements, with the dosage and duration determined by a healthcare provider based on the severity of the deficiency.