What Vitamin D Does in the Body
Vitamin D is a fat‑soluble nutrient that the body can store and even synthesize with sunlight. Its most active form, calcitriol, helps regulate calcium and phosphate, supporting bone health. But vitamin D does much more: it influences muscle function, immune response, nerve signaling, and possibly mood. Adequate levels are important not just for bones and teeth but also for overall health and resilience against infections and certain chronic diseases.
How Do We Measure Vitamin D Status?
Vitamin D status is most commonly assessed by measuring 25‑hydroxyvitamin D in the blood. Values can fluctuate seasonally, especially in regions with long, dark winters. Very low levels may indicate a deficiency, but a single low reading does not always prove a long‑term problem. Doctors often watch trends over time and consider symptoms, sun exposure, diet, and health conditions when interpreting the results.
There is no universal consensus on exact cutoffs; some labs define deficiency as below 20 ng/mL, while others use suboptimal ranges or reserve “severe deficiency” for under 10 ng/mL. Many experts suggest a target of about 30 ng/mL or higher, with some recommending 50–70 ng/mL for optimal health. Guidance can vary, reflecting differing methodologies and populations studied.
Vitamin D Deficiency Symptoms: Who Sees What
The symptoms can be subtle at first and may resemble other conditions. Here’s how deficiencies commonly present in different groups.
In Children
Children rely on vitamin D for growing bones and teeth, and a long‑standing shortage can lead to rickets, with softened bones and deformities. Other signs include slower bone growth, reduced muscle strength, muscle cramps, higher infection risk, and, in severe cases, skeletal misalignment such as bowed legs or spinal curvature. In infants, muscle cramps can be an early signal, sometimes linked to maternal vitamin D status during pregnancy.
In Adults and Seniors
Adults may notice bone or joint pains, especially in the spine, pelvis, and legs. Muscle weakness and reduced physical performance are common complaints. There is also evidence linking low vitamin D with higher risks of certain chronic diseases and infections, though the exact causal relationships remain under study. In older adults, low levels can contribute to bone loss (osteopenia or osteoporosis) and increase fracture risk, as skin becomes less efficient at producing vitamin D with age.
Who Is at Risk?
Several groups are more likely to have insufficient vitamin D. People who spend little time outdoors, wear clothing that covers most skin, or live at higher latitudes are at greater risk due to reduced sun exposure. Individuals with darker skin may require longer sun exposure to synthesize the same amount of vitamin D. People with digestive, liver, or kidney diseases that affect absorption or metabolism, and those on certain medications, may also be more susceptible. Diet alone supplies only a portion of daily needs, making sun exposure and supplementation important for many.
Prevention and Testing: What to Do
If you’re at risk, discuss vitamin D testing with your healthcare provider. Regular testing is especially important for people with malabsorption, liver or kidney disease, or those on drugs that affect vitamin D metabolism. Prevention focuses on a combination of safe sun exposure, food sources, and supplementation when needed.
Vitamin D can be found in fatty fish, fortified dairy and plant milks, eggs, and fortified cereals. Small amounts come from sunlight, but sun exposure should be balanced with skin cancer risk. In some cases, doctors may recommend vitamin D supplements to achieve and maintain target blood levels, particularly in winter months or for people with limited sun exposure.
What If Vitamin D Is Too High?
Excessive intake over time can raise calcium levels in the blood, potentially causing symptoms such as loss of appetite, nausea, weakness, irritability, and high blood pressure. Very high vitamin D levels can lead to calcium deposition in organs like the kidneys and lungs, which requires medical attention and stopping supplementation.
Bottom Line
Vitamin D is essential for bone health, muscle function, and immune support. Recognizing symptoms early, testing when risk is present, and using a combination of sun, diet, and targeted supplements can help maintain healthy vitamin D levels and reduce related health risks. If you notice persistent bone or muscle discomfort, infections, or other symptoms described here, consult a healthcare professional for evaluation and personalized advice.
