From “Low D” to Data-Driven Care: A Clinician’s Guide to Vitamin D Deficiency

Vitamin D Deficiency Is Still Prevalent in the US

Vitamin D has been popular in the wellness world for a long time. You’ll find it in supplements, smoothies, and even in jokes about getting enough sun. Still, vitamin D deficiency is surprisingly common in the U.S. 

Almost 40% of adults are thought to have low vitamin D levels, and about 20% meet the criteria for deficiency, depending on where the cutoff is set. 

Moderate and long-term low vitamin D levels are still common, especially among older adults, people with darker skin, those with obesity or absorption problems, and anyone who spends long winters with little sun. In short, this problem isn’t going away by itself. 

Vitamin D is tricky because symptoms like tiredness, low mood, muscle aches, or bone pain are easy to blame on stress, aging, or just making it through winter. Without testing, these deficiencies can stick around and affect your bones, immune system, and metabolism. 

Dr. Mitch Ghen, Access Labs' Director or Physician Consultations says, “Before we debate thresholds, we have to agree on the biomarker. In clinical practice, Serum 25-hydroxy vitamin D (25[OH]D) remains the best snapshot of vitamin D status.” 

That’s why vitamin D should be considered along with things like inflammation, metabolism, hormones, and the seasons. In this article, we’ll explain why vitamin D deficiency is still so common, who should get tested, and how lab results may help guide care. 

Explore Access Labs’ Wellness panels to test vitamin D alongside inflammation, metabolic, and hormone markers in one order. 

Key Takeaways 

• Vitamin D deficiency is still common in the U.S., even among people who take supplements regularly.
• A blood test of 25-hydroxy vitamin D helps confirm whether intake translates into healthy levels.
• Risk is higher with limited sun exposure, aging, absorption issues, metabolic conditions, and certain chronic illnesses.
• Treatment works best when it combines lifestyle habits, diet, supplementation, and follow-up testing.
• Examining vitamin D alongside inflammation, metabolic, and hormone markers helps guide next steps. 

Here's what you'll find in this article:

• Why Vitamin D Deficiency Is Still Common in the U.S.
• Which Patients Should You Test for Vitamin D Deficiency?
• Building a Personalized Treatment Plan for Vitamin D Deficiency
• How Access Labs Supports Vitamin D Testing and Monitoring
• Vitamin D Deficiency FAQs
• Putting Vitamin D Test Results to Work 

Why Vitamin D Deficiency Is Still Common In The US

Vitamin D behaves differently from many nutrients clinicians routinely monitor. As a fat-soluble vitamin, it is stored in adipose tissue and can remain deceptively low without producing obvious symptoms for months or even years. That makes deficiency easy to miss unless it’s measured directly. As Dr. Mitch Ghen explains, clinicians frequently see low vitamin D levels persist even when patients are supplementing, due to factors such as absorption challenges, impaired metabolic conversion, medication interactions, obesity, and individual differences in how vitamin D is utilized. Over time, these chronically low levels may influence bone integrity, immune signaling, and metabolic regulation, reinforcing why vitamin D status deserves closer scrutiny rather than assumptions based on intake alone.

So why is vitamin D deficiency still so common, even with all the supplements and awareness today? 

Many Americans don’t get enough sun. Working indoors, using sunscreen, living in northern areas, and long winters all make it harder for the skin to make vitamin D. In much of the country, getting enough sun just isn’t possible for months at a time. 

Skin color also plays a role. People with darker skin produce less vitamin D from the same amount of sunlight due to higher melanin content. Without sufficient vitamin D from food or supplements, the risk of deficiency increases, especially in areas with limited sun exposure. 

Metabolism and absorption matter too. Obesity can trap vitamin D in fat, reducing its levels in the blood. Conditions like celiac disease, inflammatory bowel disease, bariatric surgery, and liver or kidney disease can make it harder to absorb or use vitamin D, so regular supplements might not work as well. 

Aging also affects vitamin D. Older adults produce less vitamin D from sunlight and often spend less time outdoors. People in care facilities or with limited mobility are at even greater risk. 

There’s also a link between vitamin D, the seasons, and mood. Vitamin D plays a role in supporting normal serotonin function, and lower levels may contribute to  why people feel more tired or down in the winter. Many people attribute low energy or mood to stress or aging, but vitamin D may be a factor. 

These factors explain why vitamin D deficiency is widespread. This is also why testing for vitamin D alone might not capture the full scope. 

A more complete lab approach can help. By assessing vitamin D, inflammation, heart health, and hormone levels, Access Labs’ Wellness panels may help doctors identify patterns. This way, providers can see how vitamin D relates to other health factors and make more informed, targeted care decisions. 

Which Patients Should You Test For Vitamin D Deficiency?

Vitamin D testing doesn’t have to be done for everyone, every time, to be useful. Most guidelines don’t recommend routine screening for everyone, but they do support testing for individuals with clear risk factors or bone-related concerns. 

Vitamin D affects bone strength, muscle function, immune regulation, and metabolic health. When levels are low, signs like nagging fatigue, aches that feel like getting older, and mood dips that show up every winter, like an unwanted calendar reminder, can often be overlooked. 

Here are the populations who should strongly be considered for Vitamin D testing: 

• Older adults, especially those over 50 or 65, tend to have lower vitamin D levels because the body produces less vitamin D from sunlight as we age.
• Anyone with osteoporosis, osteopenia, or fragility fractures, since vitamin D status is important for bone support and treatment planning.
• People with chronic kidney or liver disease, as these conditions can interfere with vitamin D processing and activation.
• Those with malabsorption conditions like celiac disease or IBD, or anyone who has had bariatric surgery, should be aware that absorption isn’t always reliable.
• People with darker skin who also get limited sun exposure, which frequently occurs in northern states during winter months, or who have mostly indoor routines.
• Anyone with obesity, diabetes, or metabolic syndrome, since vitamin D can be less available in the blood and is often part of a bigger metabolic picture.
• Patients with autoimmune or chronic inflammatory conditions, since vitamin D is usually one element of a larger evaluation. 
• Patients with hormonal imbalances, including thyroid dysfunction, perimenopause or menopause, or low testosterone, since vitamin D is often evaluated alongside hormone markers involved in metabolism, bone turnover, and immune signaling.

Access Labs’ Comprehensive Male & Female Hormone panels include markers for inflammation, metabolic health, so you can connect the dots faster and take the following actions that fit the person you’re helping. 

Building a Personalized Treatment Plan for Vitamin D Deficiency 

After identifying vitamin D deficiency, the next step is to guide patients back to healthy levels. 

An effective approach combines lifestyle changes, nutritional guidance, clinically supported supplementation, and regular monitoring, adjusted to each patient’s unique health status and risk factors. 

Lifestyle and Sunlight

Getting outside can help your body make vitamin D naturally, especially in the brighter months. But for a lot of people, it’s not that simple. Where you live, the season, how much time you spend indoors, and smart skin-cancer precautions can all limit how much vitamin D you’ll actually produce from sunlight.

Optimizing Dietary Sources

Foods such as fatty fish, fortified products, and eggs provide vitamin D, yet even a well-balanced diet may not deliver enough, particularly for those following vegan diets, individuals with dietary restrictions, or anyone experiencing absorption challenges. 

According to Dr. Mitch, supporting gut health can significantly enhance the absorption of vitamin D and other nutrients. When digestion or absorption is compromised, simply increasing dietary intake may not be effective, which is why a comprehensive view of nutrition and digestive health is important. 

Supplementation

Certain patients may respond best to daily supplementation. Others may benefit from weekly regimens. In most cases, treatment begins with a higher initial dose to correct the deficiency, followed by a maintenance plan to keep up healthy levels. 

Ongoing Monitoring

Follow-up testing of vitamin D after several months is essential to confirm progress. If levels have not improved, it may be necessary to reexamine dosage, adherence, absorption efficiency, or investigate other underlying influences. 

How Access Labs Supports Vitamin D Testing and Monitoring

Vitamin D testing works best when it is easy to order, interpret, and track over time. This is the standard Access Medical Labs aims to meet. 

As a CLIA-certified, high-complexity lab, Access Labs delivers results fast and offers a testing menu designed for ongoing patient management. The goal is to provide functional medicine practitioners with reliable data to set baselines, monitor trends, and make well-informed adjustments. 

When it comes to vitamin D, Access Labs provides: 

• Testing for 25-hydroxy vitamin D (D2 and D3) for both first-time assessments and follow-up checks
• Comprehensive nutrient testing that checks vitamins B12, folate, magnesium, and zinc. These nutrients often interact with one another and can affect patient well-being and treatment response.
• Wellness panels that show vitamin D results together with markers for inflammation, cardiometabolic health, and hormones 
• Hormone Panels, which may include thyroid markers, sex hormones, adrenal hormones, and related binding proteins, to help contextualize vitamin D status within broader hormonal and metabolic patterns.

By including vitamin D and related biomarkers, Access Labs helps clinicians track patterns over time rather than relying on single readings. This approach makes it easier to see what is causing changes, how patients are responding, and when to adjust treatment plans, without complicating the workflow. 

Vitamin D Deficiency FAQs

How Often Should Vitamin D  Be Checked After Starting Supplements?

A common approach is to recheck vitamin D after a few months to see whether levels are moving in the right direction, then adjust dose and timing as needed. The best timing depends on where the patient started, the dose they’re taking, and whether they have risk variables, including malabsorption, kidney disease, or very low baseline levels.

Is It Possible To Get Too Much Vitamin D?

Yes. It’s unusual, but possible. It usually shows up when someone stays on high-dose vitamin D for a long stretch. When vitamin D gets too high, calcium can climb too, and that’s when people may start feeling off with nausea, constipation, brain fog or confusion, and in more difficult situations, kidney issues. The risk goes up with “megadose” routines and for patients with certain conditions, including kidney disease. Use labs to guide dosing, then recheck to confirm you’re in a good range. 

Is Vitamin D Testing Helpful if a Supplement is Already in Use?

Often, yes. Some patients remain low because absorption is not consistent. This may be due to gut conditions, a history of bariatric surgery, medications, or body size. Long-term higher dosing can push levels above the intended range.  

Putting Vitamin D Test Results To Work

Vitamin D is one of those nutrients people assume they’ve got covered between a multivitamin, a few sunny days, or a supplement they started years ago and never revisited. But low vitamin D is still common. The signs can be easy to miss, and taking a pill doesn’t always mean your levels are where you want them. 

A good starting point is to test vitamin D to get a baseline. From there, build a plan that fits the person in front of you, sun exposure when it’s realistic, food sources when they help, and supplementation when it’s needed. Then recheck after a few months to see what changed and adjust the plan based on the results. 

Access Labs’ Wellness panels support this approach by putting vitamin D results in context with other markers, so providers can make more informed, targeted decisions. Vitamin D can also be added to providers own custom panels at any time. 

Disclaimer: Content on the Access Labs blog is for informational purposes only and reflects the views of individual contributors, not necessarily those of Access Medical Labs. We do not endorse specific treatments, products, or protocols. This content is not a substitute for professional medical advice. Always consult a qualified healthcare provider regarding any medical concerns.

About Access:

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