Vitamin D: Why This Everyday Nutrient Matters More Than You Think

Vitamin D is often called the “sunshine vitamin,” but its role in the body goes far beyond time spent outdoors. From supporting bone strength to playing a role in immune and lung health, vitamin D is essential for many systems to function properly. Yet studies suggest that nearly 40% of adults may not get enough of it — often without realizing it.

Here’s what current research tells us about vitamin D, who may be at risk for deficiency, and why it matters for overall and respiratory health.

What Does Vitamin D Do in the Body?

Vitamin D helps the body absorb calcium and phosphorus, minerals that are critical for maintaining strong bones and teeth. It also supports immune system function, muscle strength and balance, nerve signaling, and inflammation regulation.

Without adequate vitamin D, the body struggles to use calcium efficiently, which can weaken bones and increase fracture risk over time.

Vitamin D and Immune Health

Vitamin D plays an important role in helping the immune system respond to infections. Research shows that low vitamin D levels are associated with increased susceptibility to respiratory infections, including seasonal influenza.

One study found that vitamin D supplementation during winter months reduced flu infections among school-aged children, highlighting its role in immune defense when sunlight exposure is limited.

While vitamin D is not a cure or substitute for vaccines or medical treatment, experts agree that adequate levels are necessary for normal immune response.

Bone Health and Muscle Strength

Vitamin D is essential for preventing bone loss and maintaining skeletal strength throughout life.

Low levels have been linked to osteoporosis, osteomalacia (the softening of bones in adults), and a higher risk of falls and fractures, particularly in older adults. In children, severe deficiency can lead to rickets, a condition that impairs bone development and growth.

Mental Health and Mood

Studies have found an association between low vitamin D levels and depression, though researchers are still determining whether deficiency contributes to mood disorders or occurs as a result of them.

Some evidence suggests that correcting low vitamin D levels may help improve mood symptoms in certain individuals, but research is ongoing.

Who Is at Higher Risk for Vitamin D Deficiency?

Certain groups are more likely to have low vitamin D levels, including adults over age 50, people with darker skin pigmentation, those who live in northern climates or have limited sun exposure, and individuals with obesity. 

Risk is also higher among people with gastrointestinal conditions that impair nutrient absorption, such as Crohn’s disease or celiac disease, as well as those who have undergone gastric bypass surgery. Because vitamin D is fat-soluble, any condition that interferes with fat absorption can significantly reduce the body’s ability to use it.

How to Get Enough Vitamin D

• Sunlight ☀️

The body produces vitamin D when skin is exposed to sunlight. About 15–20 minutes of sun exposure, several times per week, may be enough for some people — but sunscreen, skin tone, latitude, and season all affect vitamin D production. Experts emphasize that sun protection remains essential to reduce skin cancer risk.

• Food Sources 🐟

Vitamin D can also be obtained through diet, particularly from foods such as fatty fish including salmon, tuna, and sardines, as well as cod liver oil and egg yolks. Many commonly consumed products are also fortified with vitamin D, including milk, yogurt, orange juice, and certain breakfast cereals, making them accessible sources for people who may have limited sun exposure.

• Supplements 💊

Supplements may be necessary for people who cannot maintain adequate levels through sun exposure or diet alone. However, too much vitamin D can be harmful, so supplementation should be guided by a healthcare provider and blood testing when appropriate.

When to Consider Testing

A simple blood test can be used to measure vitamin D levels, and testing may be recommended for people who have bone or muscle pain, experience frequent infections, have osteoporosis or a history of fractures, are homebound or avoid sun exposure, or have medical conditions that affect nutrient absorption.

The Bottom Line

Vitamin D supports bone strength, immune function, muscle health, and overall well-being. While it’s not a cure-all, maintaining healthy levels is an important part of long-term health — especially for individuals with chronic conditions or limited sun exposure.

If you’re concerned about vitamin D deficiency, talk with your healthcare provider about testing and safe ways to maintain healthy levels.

Ferrer Pulmonary Institute

If you or a loved one have questions about lung health or want expert guidance on respiratory care, Ferrer Pulmonary Institute is here to help.

Our team takes a personalized, whole-patient approach to pulmonary care, supporting long-term respiratory health and overall well-being. Learn more or schedule a consultation today.