Tired All the Time? Vitamin D Deficiency Could Be Why

Fatigue is one of the most common complaints doctors hear. Patients describe it in different ways, exhausted all the time, dragging through the day, waking up tired no matter how many hours they sleep, needing caffeine just to function. The causes are many, but one that gets missed more often than it should is vitamin D deficiency.

It’s one of the most common nutritional deficiencies in the United States affecting an estimated 40% of adults and one of the most underdiagnosed, because the symptoms are so easy to attribute to everyday life.

What vitamin D actually does

Vitamin D isn’t just a bone mineral. It functions more like a hormone, playing roles in immune regulation, muscle function, mood, cardiovascular health, and energy metabolism at the cellular level. Almost every tissue in the body has vitamin D receptors.

When levels drop too low, the effects ripple through multiple systems, which is why vitamin D deficiency doesn’t cause one distinct symptom. It causes a cluster of vague ones that are easy to wave off.

The symptoms worth paying attention to

Vitamin D deficiency can look like many things:

Persistent fatigue and low energy: Not just tired after a poor night’s sleep, but a bone-deep exhaustion that doesn’t improve with rest. Research has shown that people with very low vitamin D levels report significantly more fatigue than those with sufficient levels, even when controlling for sleep quality and other factors.

Muscle weakness and aches: A dull, general achiness, especially in the back, legs, and joints is frequently associated with low vitamin D. It’s often mistaken for getting older, overexertion, or fibromyalgia.

Frequent illness: Vitamin D is central to immune function. People who are deficient tend to get colds, respiratory infections, and other bugs more often and take longer to recover.

Low mood and depression: There’s a well-established link between low vitamin D and depression, particularly seasonal affective disorder. The mechanism isn’t fully understood, but the correlation is consistent across multiple studies.

Brain fog and difficulty concentrating: Some people describe difficulty focusing, forgetfulness, or a mental “haziness” that improves once vitamin D levels are corrected.

Bone pain and slow-healing injuries: At more severe levels of deficiency, bone pain becomes more prominent and stress injuries take longer to heal.

Who is most at risk?

Vitamin D is produced by your skin in response to sunlight, which means anything that reduces sun exposure or skin’s ability to make it raises your risk.

High-risk groups include:

• People who spend most of their time indoors (office workers, people with mobility limitations)
• Darker skin tones, melanin reduces the skin’s ability to produce vitamin D from sunlight
• People over 65, whose skin produces vitamin D less efficiently
• People who live in northern climates or areas with frequent cloud cover, though Memphis’s latitude helps, it’s not enough if you’re mostly indoors
• People who are overweight, vitamin D is fat-soluble and gets sequestered in fat tissue
• People with digestive conditions (Crohn’s, celiac, IBS) that affect absorption
• People who avoid dairy, fatty fish, and fortified foods
• Pregnant or breastfeeding women, whose needs increase significantly

How vitamin D deficiency is diagnosed

Diagnosis is straightforward: a simple blood test measuring your 25-hydroxyvitamin D level. Most clinicians consider anything below 20 ng/mL deficient, and below 30 ng/mL insufficient. You don’t need to fast beforehand.

The test is often included in a routine blood panel, but you may need to request it specifically, it’s not always part of a standard annual workup.

Treatment

For most people, vitamin D deficiency is highly treatable:

Supplementation: Vitamin D3 supplements are widely available and inexpensive. Dosing depends on how deficient you are; severely deficient patients may start on a high weekly prescription dose before transitioning to a maintenance dose. Your doctor should guide this, too much vitamin D over time can cause toxicity.

Dietary changes: Good food sources include fatty fish (salmon, sardines, mackerel), egg yolks, and fortified foods (dairy milk, plant milks, orange juice, cereals). Food alone rarely corrects a significant deficiency but helps maintain levels.

Sun exposure: 10–20 minutes of midday sun on bare arms and legs several times a week produces meaningful vitamin D. Sunscreen blocks production, so brief unprotected exposure before applying sunscreen is a reasonable balance. This alone is rarely enough to correct deficiency.

When to get checked

Make an appointment if you recognize yourself in the symptoms above, especially if the fatigue has been going on for weeks or months without a clear cause, or if you have multiple risk factors. It’s a quick blood test with a straightforward fix if deficiency is confirmed.

Don’t just buy supplements without testing first. Vitamin D deficiency and vitamin D toxicity both cause symptoms, and treating without knowing your level means guessing.

How Beloved Medical can help

We can include vitamin D testing as part of routine bloodwork for patients who come in for annual physicals or with fatigue If you have vitamin D deficiency, we’ll build a supplementation and monitoring plan and recheck your levels after a few months to confirm improvement.

We’re a family practice in Cordova, TN. Same-day appointments are often available, and we accept most major insurance.

To schedule a visit:

• Call (901) 249-0847
• Or book an appointment online

This blog post is for informational purposes only and does not replace professional medical advice. Please consult a healthcare provider before beginning any supplement regimen.