Can Lack of Vitamin D Cause Calcium Deficiency?

October 25, 2025 •

3 min read

According to the Cleveland Clinic, a severe and chronic vitamin D deficiency can lead to hypocalcemia, or low blood calcium levels. It is well-established that vitamin D is essential for the body's proper absorption of calcium, making a lack of one a direct cause of a deficiency in the other.

Quick Summary

Chronic or severe vitamin D deficiency significantly reduces the body's ability to absorb calcium from the diet, leading to low blood calcium levels (hypocalcemia). The body attempts to correct this by taking calcium from bones, which can result in conditions like osteomalacia and osteoporosis.

Key Points

Vitamin D is a Regulator: The primary function of active vitamin D (calcitriol) is to regulate and significantly increase the body's intestinal absorption of calcium.
Low Vitamin D, Low Absorption: Without sufficient vitamin D, the body's ability to absorb dietary calcium is drastically reduced, leading to low blood calcium (hypocalcemia).
Bone Sacrifice: To compensate for low blood calcium, the body releases parathyroid hormone (PTH), which signals the body to pull calcium from the bones, weakening them over time.
Risk of Bone Diseases: This compensatory process leads to bone disorders such as rickets in children and osteomalacia and osteoporosis in adults.
Treatment is Possible: A dual deficiency can be treated with a combination of dietary adjustments, controlled sun exposure, and vitamin D and calcium supplements under medical supervision.
Symptoms Serve as a Warning: Common symptoms like fatigue, muscle weakness, and bone pain often signal a vitamin D and calcium imbalance and should prompt a medical evaluation.

Vitamin D, often called the “sunshine vitamin,” is actually a hormone vital for maintaining the body's mineral balance, with a key role in calcium regulation. Although dietary calcium intake is important, the body cannot effectively utilize it without sufficient vitamin D. A significant deficiency in vitamin D can therefore directly lead to calcium deficiency.

How Vitamin D Facilitates Calcium Absorption

The relationship between vitamin D and calcium is metabolic. Calcium consumed in the diet is absorbed through the intestines, a process regulated by the active form of vitamin D, calcitriol. Low vitamin D levels compromise calcitriol production, impairing calcium absorption and causing a drop in blood calcium.

To correct low blood calcium, the parathyroid glands release parathyroid hormone (PTH). PTH stimulates bone resorption, releasing calcium from bones into the bloodstream. It also increases calcium reabsorption in the kidneys and attempts to activate remaining vitamin D. While this maintains blood calcium, it depletes bone calcium, potentially leading to long-term bone health issues.

Impact on Bone Health

Persistent low vitamin D and calcium levels can cause rickets in children, characterized by soft bones and skeletal deformities. In adults, this can lead to osteomalacia, causing bone pain and muscle weakness, and increasing the risk of osteoporosis, which makes bones brittle and prone to fractures.

Comparison: Vitamin D vs. Calcium Sources


Feature	Vitamin D Sources	Calcium Sources
Primary Source	Sunlight (UVB exposure)	Dairy products (milk, cheese, yogurt)
Secondary Sources	Fatty fish (salmon, tuna), fortified milk/cereals	Leafy greens (kale, broccoli), fortified juices, tofu
Storage in Body	Stored in fat cells	Primarily stored in bones and teeth
Role in Absorption	Essential for calcium absorption in the intestines	The mineral being absorbed
Deficiency Risk	Common due to lack of sun or diet	Often caused by vitamin D deficiency or low dietary intake

Recognizing the Signs

Symptoms of a combined deficiency can overlap and may include fatigue, muscle weakness and cramps, bone pain, changes in hair and skin, numbness or tingling, and mood changes. Seeking medical advice for diagnosis and treatment is recommended.

Addressing the Deficiency

Correcting a deficiency often involves dietary changes, increasing intake of vitamin D and calcium rich foods, and potentially taking supplements. Sensible sun exposure can also aid vitamin D production. A healthcare provider can determine the best course of action based on blood test results.

Conclusion

A lack of vitamin D is a direct cause of calcium deficiency due to vitamin D's essential role in calcium absorption. The body's attempt to maintain blood calcium by drawing from bone reserves can lead to significant bone health problems like rickets, osteomalacia, and osteoporosis. Maintaining adequate levels of both nutrients through diet, safe sun exposure, and supplementation is crucial for bone density and overall health. The interdependence of vitamin D and calcium highlights the importance of a balanced approach to nutrition and preventative care.

For more detailed information on bone metabolism and calcium homeostasis, consider reviewing the comprehensive article found on the National Institutes of Health (NIH) website: The role of vitamin D in the endocrinology controlling calcium and phosphate metabolism.

Frequently Asked Questions

While the body has compensatory mechanisms, a severe or chronic vitamin D deficiency will eventually lead to calcium deficiency. For most people, it's a gradual process, but the effects of bone depletion can start relatively soon after vitamin D levels drop significantly.

It is challenging to obtain sufficient vitamin D from diet alone, as very few foods naturally contain the nutrient in high amounts. Fortified foods help, but many doctors recommend supplements, especially for those with limited sun exposure.

The primary function of vitamin D is to regulate calcium homeostasis by increasing the efficiency of intestinal calcium absorption. Without it, the body can only absorb a small fraction of the calcium consumed.

Early signs can be non-specific and subtle, and in some cases, people may not experience any symptoms at all. As the condition progresses, symptoms may include fatigue, muscle aches, and bone pain.

Yes, older adults are at a higher risk. This is because their skin's ability to produce vitamin D from sunlight declines with age, and their intestinal calcium absorption also decreases.

Your vitamin D levels can be checked with a simple blood test that measures the concentration of 25-hydroxyvitamin D in your blood. A healthcare provider can order and interpret this test.

While calcium supplements are important, they will not be effectively absorbed if your vitamin D levels are insufficient. For this reason, combination supplements or addressing the vitamin D deficiency first is often necessary.