Why Your Vitamin D Levels Aren’t Improving — Even If You Supplement Consistently

Vitamin D is one of the most commonly recommended supplements today because of its essential role in:

• Bone density and skeletal strength

• Immune health

• Brain and nervous system support

• Neurotransmitter and neuromuscular function

• Cardiometabolic health

• Hormone regulation

Yet many people take Vitamin D faithfully for months and still see little improvement in blood levels or symptoms. Some even need extremely high doses just to avoid deficiency. Low Vitamin D values vary depending on the lab measuring your levels, but most say you are deficient when your blood levels of Vitamin D are below 20 or 30ng/mL. However, if you speak with a practitioner who is looking to optimize levels instead of barely squeaking by, the target range is typically between 50-80ng/mL. 

If you have been taking Vitamin D supplements for a while without seeing much improvement in your blood levels, here are three major reasons this may be happening:

1️⃣ The type of Vitamin D you’re taking may limit absorption
2️⃣ The form and delivery method may not be ideal for your body
3️⃣ You may be missing key cofactors that help your body actually use Vitamin D

Let’s break this down and help you optimize your Vitamin D levels with a few smart adjustments.

Not All Vitamin D Is the Same: D2 vs. D3

There are two primary forms of Vitamin D:

✔️ Vitamin D2 (Ergocalciferol)

• Plant-derived

• Commonly used in fortified foods

• Less biologically active

• Raises Vitamin D slowly

• Levels are harder to maintain

✔️ Vitamin D3 (Cholecalciferol)

• The form your body naturally produces from sunlight

• Found in animal-based foods and high-quality supplements

• More stable, better absorbed, and more effective

• Maintains blood levels more reliably

Despite this, Vitamin D2 is still commonly prescribed in extremely high weekly doses (like 50,000 IU), mainly because it was the first form approved for prescription use. However, today we have strong evidence showing Vitamin D3 is significantly more effective.

👉 Bottom line: Always make sure your supplement is Vitamin D3, not D2.

The Delivery Method Matters More Than You Think

Quality matters with all supplements—and Vitamin D is no exception.

While capsule forms generally absorb well in a healthy digestive system, many factors can interfere with absorption, including:

• Low stomach acid

• Poor bile production

• Gut inflammation

• Digestive infections (bacterial, fungal, or parasitic)

• Malabsorption issues

If any of these are present, your body may struggle to pull Vitamin D from capsules.

✔️ When Sublingual (Under-the-Tongue) Vitamin D Is Better

Sublingual Vitamin D absorbs directly into circulation, bypassing the digestive tract. This can:

• Improve absorption speed

• Increase overall dosage actually absorbed

• Reduce dependency on gut function

If you’ve battled chronically low Vitamin D despite supplementing, sublingual drops may be a better option.

Don’t Forget the Cofactors: Your Body Needs More Than Just Vitamin D

Vitamin D doesn’t work alone. It requires nutritional partners called cofactors to activate and function properly in the body.

The Most Important Vitamin D Cofactors Include:

✔️ Magnesium

• Helps convert Vitamin D into its active form

• Often the most important missing piece

• Increasing magnesium alone can dramatically improve Vitamin D levels

✔️ Zinc

• Supports Vitamin D signaling and utilization

✔️ Vitamin K2

• Helps Vitamin D properly regulate calcium

• Prevents calcium buildup in soft tissues

• Supports strong bones and teeth

✔️ Vitamin A

• Works synergistically with Vitamin D

• Found naturally with Vitamin D in cod liver oil

• Ideal balance is roughly a 10:1 ratio of Vitamin A : Vitamin D

Because Vitamin A and D are fat-soluble, they are typically best absorbed when taken with food or healthy fats (including omega-3s or fish oil).

👉 Bottom line: If you’re only taking Vitamin D without its cofactors, your body may not be able to effectively use it — leading to chronically low levels no matter how much you take.

Want to Optimize Your Vitamin D Safely and Effectively?

Before increasing your dose, switching brands endlessly, or giving up on supplementation altogether, first make sure you are:

• Taking Vitamin D3, not D2

• Using a high-quality supplement

• Considering sublingual delivery if absorption is an issue

• Supporting Vitamin D with magnesium, zinc, K2, Vitamin A, and Omega-3's

To make this easy, here are some of my most trusted supplement options:

👉 My recommended Vitamin D support options:

Vitamin D Optimization Supplements

Final Note

Always consult with your healthcare provider before making major supplement changes, especially if you have chronic conditions, take prescription medications, or have unique health needs.

If you’d like personalized guidance, testing, or a tailored plan, I’d be happy to help.