Vitamin D3: The Hormone Athletes Shouldn't Overlook

Vitamin D supports bone health and normal muscle function, and northern winters can limit production from sunlight. Correcting deficiency can matter; taking extra when you are already sufficient has not consistently improved strength.

Start with your total intake and individual needs. The dose and testing sections below explain the standard intakes, upper limit, and why a high-dose podcast routine is not a universal athlete prescription.

Vitamin D3 is more than just a vitamin

UVB sunlight allows skin to produce vitamin D3. The liver converts it to 25-hydroxyvitamin D, the form measured in blood tests; the kidneys and other tissues then help produce the active form, calcitriol.

Calcitriol is a secosteroid hormone that binds vitamin D receptors and influences gene expression. This does not mean D3 behaves like testosterone or that taking more builds muscle like an anabolic hormone.

Dr. Rhonda Patrick discusses this receptor signaling and the importance of adequate vitamin D in a Huberman Lab discussion.

Why athletes should pay attention to vitamin D3

Muscle function and strength

Vitamin D contributes to normal skeletal muscle function. Significant deficiency can cause weakness, and correcting it may help restore normal function. Extra D3 in people who are already sufficient has not consistently improved strength.

Bone health

Vitamin D helps regulate calcium and phosphorus. Deficiency can impair bone mineralization, and severe deficiency can cause bone pain and weakness. Adequacy is relevant when training places heavy loads on the skeleton or bone stress injuries are a concern.

Recovery and immune function

Vitamin D influences immune signaling and normal tissue function. Research has not established that high doses directly accelerate muscle recovery or prevent overtraining.

Hormones and testosterone

Low vitamin D and low testosterone have been associated in studies, but supplementation trials have not consistently shown meaningful testosterone increases in otherwise healthy men. I would not use D3 as a testosterone booster.

Living in the Midwest changes the conversation

Winter changes the picture for those of us in Minnesota, Wisconsin, and the Dakotas. Short days, covered skin, and the sun's angle can all limit vitamin D production.

A classic study found that Boston winter sunlight failed to produce measurable previtamin D3 in experimental skin samples from November through February. Minnesota is farther north, so time outdoors in winter does not guarantee meaningful production.

Diet and supplementation become more important sources when skin production drops. That does not establish a need for a massive dose, and summer sunlight does not guarantee adequate status throughout winter.

Ordinary window glass blocks UVB. Daylight through a window may support your circadian rhythm, but it does not stimulate vitamin D production.

As we age, vitamin D becomes even more important

Aging makes skin less efficient at producing vitamin D3 from sunlight. That is different from saying everyone becomes worse at absorbing supplements; digestive conditions, medications, and other individual factors can affect absorption.

Maintaining muscle, bone health, and physical function into your 40s, 50s, 60s, and beyond includes appropriate nutrition. Adequate vitamin D is one part of that work.

How much vitamin D3 should athletes take?

This is where opinions vary considerably.

The current U.S. recommended dietary allowance is:

• Ages 19–70: 600 IU daily
• Ages 71 and older: 800 IU daily

Those amounts are total daily intake from food and supplements and assume minimal sun exposure. They are designed to meet the nutritional needs of most people, not specifically to optimize strength performance. A separate, higher requirement for athletes has not been established.

You'll also see athletes and health educators discussing considerably higher amounts.

During a March 23, 2026 Huberman Lab conversation, Andrew Huberman described taking approximately 5,000–8,000 IU of vitamin D3 daily.

Dr. Rhonda Patrick said she takes around 5,000 IU per day.

Both discussed supplementation in the context of their individual health routines, and Huberman mentioned using bloodwork to guide his decisions.

What about 5,000 IU daily?

I think 5,000 IU is a dose worth discussing with a clinician when there is documented low vitamin D status or another medical indication. Minimal sunlight exposure alone does not establish a need for that dose.

But it's important to understand what that number means.

5,000 IU daily is above the established adult tolerable upper intake limit of 4,000 IU from food and supplements combined.

That doesn't mean a single 5,000 IU dose is toxic, or that 5,000 IU is never appropriate.

Some people being treated for deficiency may need doses at or above that level for a period of time under medical supervision.

But the fact that a dosage is used by Huberman or Patrick doesn't prove it's necessary, optimal, or safe indefinitely for every athlete.

The International Olympic Committee has recognized vitamin D as a nutrient of potential concern in athletes, while also noting that athlete-specific supplementation requirements haven't been firmly established.

For generally healthy adults under 75, the 2024 Endocrine Society guideline recommends against routinely exceeding standard dietary intakes without another indication.

My position is simple: take vitamin D seriously, especially in the winter, but match the dose to your actual needs.

If a higher-dose approach such as 5,000 IU is being considered, discuss individual risk factors, total intake, and appropriate testing and monitoring with a healthcare professional before starting it.

We shouldn't confuse a common supplement strength with a universally appropriate dose.

Should athletes test their vitamin D levels?

If an athlete has symptoms or risk factors suggesting deficiency, a clinician may recommend a blood test called 25-hydroxyvitamin D.

This helps assess vitamin D status.

The NIH fact sheet summarizes the National Academies' thresholds: levels of 20 ng/mL or higher are generally adequate for most people's bone-health needs, while levels below 12 ng/mL indicate risk of deficiency. Levels from 12 to below 20 ng/mL may be inadequate for some people.

Some sports medicine discussions suggest higher targets, but an ideal vitamin D blood level for maximizing strength or athletic performance hasn't been established.

Routine screening is not recommended for every healthy person.

I think the key is to have a reason for testing rather than just chasing the highest blood number possible.

Should you take vitamin D3 with K2?

You'll see a lot of D3/K2 supplements marketed to athletes.

The theory is that vitamin D supports calcium absorption while vitamin K2 contributes to the activation of proteins involved in bone and vascular health.

That biological relationship is real.

But it doesn't mean vitamin D automatically deposits calcium into your arteries unless you take K2.

Research on combined D3 and K2 supplementation continues to develop, particularly in bone and cardiovascular health.

At this point, there's insufficient evidence to say every athlete taking D3 also needs supplemental K2. K2 does not make excessive vitamin D intake safe.

That said, ensuring adequate vitamin K intake makes sense.

Vitamin K is available through foods, including leafy greens and certain fermented products.

People taking warfarin or other vitamin K antagonist medications should not begin K2 supplementation without medical guidance.

What about magnesium and calcium?

These two minerals deserve attention, especially among strength athletes.

Magnesium contributes to normal muscle and nerve function and is involved in vitamin D metabolism.

If you aren't getting adequate magnesium, improving your intake is important.

Good dietary sources include nuts, seeds, beans, whole grains, and leafy greens.

But you don't need to take magnesium at the exact same time as vitamin D3.

Calcium is essential for skeletal strength and normal muscle contraction.

Vitamin D helps your body absorb it.

But that doesn't automatically mean you need to add a calcium supplement.

Many athletes can meet calcium needs through food.

I would rather see someone assess their overall diet than automatically stack D3, K2, magnesium, and calcium pills without knowing whether they're needed.

When should you take vitamin D3?

My practical preference would be breakfast or lunch.

Vitamin D is fat-soluble, so taking it with a meal containing some fat is a sensible approach.

Eggs, avocado, yogurt, salmon, nuts, or a regular mixed meal can work.

You don't need a massive amount of dietary fat.

And you don't have to take it immediately before or after training.

There is no strong evidence that vitamin D3 acts like an acute pre-workout supplement.

Consistency matters more than trying to time it around your deadlift session.

Does vitamin D3 at night affect sleep?

You'll hear claims that vitamin D3 should never be taken at night because it interferes with melatonin.

The human research doesn't currently establish that.

Vitamin D has been studied in connection with sleep regulation, and some research suggests supplementation may help subjective sleep quality in certain populations.

But that doesn't prove vitamin D taken before bed causes insomnia. Those studies do not establish an optimal morning-versus-evening dosing time.

Personally, I think taking it earlier in the day is a simple routine.

If someone notices worse sleep after taking it at night, moving it to breakfast makes sense.

But if you're taking D3 with dinner and sleeping fine, there's no compelling evidence you must change your routine.

Can you take too much vitamin D?

Absolutely.

Because vitamin D increases calcium absorption, excessive supplementation can cause abnormally high blood calcium levels.

That can lead to nausea, weakness, excessive thirst, frequent urination, kidney stones, and potentially serious kidney damage.

People with certain medical conditions or those taking particular medications may be more vulnerable.

One thing I want to make clear is that more vitamin D does not necessarily mean more benefits.

The objective is to maintain adequate vitamin D status, not to consume the highest number of international units possible.

My take for strength athletes

Vitamin D deserves attention alongside training, protein, and recovery, particularly when northern winters or aging limit skin production. Assess intake, identify deficiency when appropriate, and match supplementation to actual needs.

That does not mean automatically taking 5,000 IU daily or chasing unusually high blood levels. Some athletes may benefit from supplements; others already have adequate intake and status.

Support long-term muscle and bone health with adequate nutrition and an appropriate plan, rather than simply taking more.

— Grip & Grub | The Iron Library

Research & References

1. NIH — Vitamin D Health Professional Fact Sheet
2. Endocrine Society — 2024 Vitamin D Clinical Practice Guideline
3. Huberman Lab — Dr. Rhonda Patrick: Micronutrients for Health & Longevity
4. Huberman Lab — The Best Vitality & Health Protocols (March 23, 2026)
5. International Olympic Committee — Dietary Supplements and the High-Performance Athlete
6. Vitamin D and the Athlete-Patient: State of the Art
7. Influence of Season and Latitude on Vitamin D3 Synthesis
8. NIH — Magnesium
9. NIH — Vitamin K
10. Vitamin D Supplementation and Sleep: A Systematic Review and Meta-Analysis of Intervention Studies

This article is for educational purposes and is not a substitute for individualized medical advice.