What happens if you don't have enough vitamin D and calcium?

January 4, 2026 •

4 min read

According to the National Institutes of Health, a significant portion of the population has inadequate vitamin D levels, a deficiency that has profound implications for the body's use of calcium. This symbiotic relationship is critical, and knowing what happens if you don't have enough vitamin D and calcium is key to preventing long-term health issues.

Quick Summary

Chronic deficiency can cause serious health problems, including softened and weak bones in both children and adults, increasing the risk of fractures and osteoporosis. Beyond skeletal issues, it can also lead to muscle weakness, nerve and mood problems, and fatigue.

Key Points

Interdependence: Vitamin D is necessary for the body to absorb calcium effectively, making their partnership crucial for bone health and beyond.
Bone Weakening: Chronic deficiency leads to soft, weak bones (rickets in children, osteomalacia in adults) and porous, brittle bones (osteoporosis).
Systemic Issues: Beyond the skeleton, low levels can cause muscle cramps, nerve problems, fatigue, depression, and a higher risk of falls.
Body's Defense Mechanism: To maintain blood calcium, the body steals it from the bones, causing them to weaken over time.
Prevention and Treatment: Combating deficiency involves a balance of diet (fortified foods, dairy), safe sun exposure, and potentially supplements under a doctor's supervision.

The Essential Partnership of Vitamin D and Calcium

Vitamin D and calcium are two of the most critical nutrients for human health, working in a powerful and interconnected partnership. While calcium is the primary building block for bones and teeth, vitamin D is the facilitator, enabling the body to properly absorb and utilize that calcium. When this vital duo is lacking, a cascade of health problems can unfold, starting with the skeletal system and extending to affect muscles, nerves, and overall systemic functions.

The Critical Role of Vitamin D

Vitamin D is often called the 'sunshine vitamin' because the body produces it upon exposure to ultraviolet B (UVB) rays from the sun. Without sufficient vitamin D, the body's ability to absorb dietary calcium is drastically reduced. Normal intestinal calcium absorption is about 30–40%, but without adequate vitamin D, this drops to a mere 10–15%. This inefficiency forces the body into a state of mineral imbalance, with serious consequences.

How the Body Responds to Low Levels

When blood calcium levels drop due to poor absorption, the body has a failsafe mechanism involving the parathyroid glands. These glands release parathyroid hormone (PTH), which signals the bones to release their stored calcium into the bloodstream to maintain a stable balance. While this protects critical functions like nerve signaling and heart rhythm in the short term, it catastrophically weakens the skeletal structure over time.

The Health Consequences of Deficiency

The effects of insufficient vitamin D and calcium vary depending on age and the severity of the deficiency. They can range from subtle, non-specific symptoms to severe, life-altering diseases.

Effects on Children: Rickets

Rickets is the most well-known disease associated with vitamin D deficiency in children. Since their bones are still developing, the lack of proper mineralization causes them to become soft, weak, and deformed.

Common symptoms of rickets include:

Bowed or bent legs
Bone pain and tenderness
Skeletal deformities, such as thickened ankles and wrists
Stunted growth
Delayed motor skills
Soft skull bones
Increased risk of seizures due to very low blood calcium

Effects on Adults: Osteomalacia and Osteoporosis

In adults, a prolonged deficiency causes a related condition called osteomalacia, or soft bones. Unlike osteoporosis, which is a loss of bone mass, osteomalacia involves a defect in the bone-building process, resulting in bones that are poorly mineralized and weak.

Long-term deficiency also accelerates the development of osteoporosis, a condition that makes bones porous and brittle, dramatically increasing the risk of fractures. This is a particular concern for older adults, who are already at a higher risk of bone loss and falls.

Consequences of adult deficiencies include:

Persistent bone and back pain
Muscle weakness and cramps
Increased risk of falls and fractures from minor trauma
Osteoporosis

Beyond the Bones: Systemic Health Effects

The impact of low vitamin D and calcium extends far beyond bone health. The deficiencies are linked to a wider array of chronic and systemic health problems:

Muscle Function: Calcium is essential for muscle contraction. Low levels can lead to muscle cramps, spasms, and overall weakness. Vitamin D is also critical for optimal muscle function and strength.
Nervous System and Mental Health: Both nutrients are involved in nerve transmission. Deficiencies can cause neurological and psychological symptoms, including fatigue, depression, memory issues, confusion, and irritability.
Cardiovascular Health: Research has found associations between low vitamin D levels and a higher risk of cardiovascular disease, high blood pressure, and stroke. Severe calcium deficiency can even lead to abnormal heart rhythms or congestive heart failure.
Immune System: Vitamin D plays a significant role in modulating the immune system. Deficiency is linked to an increased susceptibility to infections and autoimmune diseases.

Comparison of Deficiency Effects


Feature	Children (Rickets)	Adults (Osteomalacia/Osteoporosis)
Primary Issue	Impaired mineralization of growing bones	Defective mineralization of existing bone (osteomalacia) or loss of bone mass (osteoporosis)
Skeletal Symptoms	Bowed legs, thickened wrists/ankles, stunted growth	Persistent bone pain, increased fracture risk, loss of height
Muscular Symptoms	Weakness, muscle pain, potential spasms/tetany	Weakness, aches, cramps, and increased fall risk
Other Symptoms	Delayed motor skills, seizures, dental problems	Fatigue, depression, memory loss, nervous system issues
Main Cause	Inadequate vitamin D/calcium intake during bone growth	Chronic low intake, poor absorption, or reduced sun exposure

Addressing the Problem

Preventing and treating deficiencies in vitamin D and calcium often involves a multi-pronged approach combining diet, sun exposure, and supplementation.

Dietary Sources: Incorporate calcium-rich foods like dairy products, leafy greens (kale, broccoli), and fortified items (cereals, juices). For vitamin D, fatty fish (salmon, tuna), egg yolks, and fortified milk are good options.
Sun Exposure: Safe, moderate sun exposure can help your body produce vitamin D naturally. However, factors like season, time of day, skin color, and location influence production, and sunscreen limits it.
Supplementation: In many cases, diet and sun exposure are not enough, and a healthcare provider may recommend supplements. Vitamin D and calcium supplements are readily available, often combined. Always consult a doctor before starting a new supplement regimen.

Conclusion

Failing to get enough vitamin D and calcium can have severe and far-reaching health implications. The combined deficiency directly compromises bone health, leading to debilitating conditions like rickets in children and osteomalacia and osteoporosis in adults. The systemic impact is also significant, affecting everything from muscle and nerve function to mood and immunity. Recognizing the symptoms early and proactively addressing them with lifestyle changes, dietary adjustments, and medical supervision is vital for preventing long-term damage and maintaining overall wellness. For more detailed information on dietary supplements, you can visit the NIH Office of Dietary Supplements.

Frequently Asked Questions

Early signs can be subtle and non-specific, including fatigue, general weakness, bone and back pain, and muscle aches or cramps. In severe cases, symptoms like tingling in the extremities, hair loss, and mood changes can occur.

A vitamin D deficiency can be confirmed with a blood test that measures your 25-hydroxyvitamin D levels. A calcium deficiency is often identified through a review of symptoms, medical history, and sometimes a bone density test, as blood calcium levels are tightly regulated.

While increasing dietary intake of vitamin D and calcium is important, it may not be enough to correct an existing deficiency, especially if it is severe. In many cases, healthcare providers recommend supplements in addition to dietary changes.

Certain groups are at higher risk, including older adults (whose skin produces less vitamin D), breastfed infants, people with darker skin, those with limited sun exposure, and individuals with conditions that affect fat absorption, like Crohn's disease or celiac disease.

You cannot get toxic levels of vitamin D from sun exposure alone. The body regulates production to prevent excess amounts. However, excessive intake of vitamin D from supplements can be harmful and lead to hypercalcemia.

Osteomalacia is the softening of the bones due to a defect in the bone-building process, most often caused by a vitamin D deficiency. Osteoporosis is a condition of low bone density and mass, which can be exacerbated by long-term vitamin D and calcium deficiency, leading to fragile, brittle bones.

Increase intake by consuming foods like fatty fish (salmon), fortified milk and cereals, egg yolks, and leafy greens. Safe sun exposure and supplements, if recommended by a doctor, are also effective ways to boost levels.