Vitamin D Does More Than Support Your Bones: Why Women Should Pay Attention to It

Vitamin D might be one of the most misunderstood nutrients in women's wellness.

On one side, it's treated like the answer to everything:

Hormones.

Mood.

Fertility.

Immunity.

Fatigue.

PCOS/PMOS.

Hair loss.

Take more vitamin D!

On the other side, we sometimes forget that vitamin D really is physiologically important.

So what's actually true?

As a biomedical engineer, this is exactly the kind of conversation I love because the answer isn't:

“Vitamin D is overhyped.”

And it isn't:

“Everyone needs a giant dose.”

It's:

Vitamin D is essential. Let's understand what it actually does.

What is vitamin D?

Vitamin D is a fat-soluble vitamin that helps regulate calcium absorption and bone mineralization and also participates in neuromuscular, immune and other cellular functions.

Your body can obtain vitamin D from:

• sunlight exposure

• certain foods

• fortified foods

• dietary supplements

But the vitamin D produced in your skin or consumed isn't immediately in its final active form.

It undergoes processing first in the liver and then primarily in the kidneys to form biologically active vitamin D.

This is one reason I sometimes describe vitamin D as more hormone-like than many people realize.

It participates in a much larger physiological system.

Why is vitamin D especially worth discussing with women?

Bone health.

Women are at increased risk of osteoporosis as they age, particularly after menopause when declining estrogen contributes to accelerated bone loss.

Vitamin D supports calcium absorption and normal bone mineralization.

That doesn't mean taking huge doses of vitamin D will magically prevent osteoporosis.

Bone health also involves:

• calcium

• resistance and weight-bearing exercise

• hormones

• genetics

• age

• smoking and alcohol exposure

• medications

• body composition

• other medical conditions

But adequate vitamin D is part of that picture.

And it's something worth thinking about long before you're 70.

What does vitamin D actually do?

Vitamin D is best established for its role in calcium metabolism and bone health.

It also participates in:

• normal muscle function

• nerve function

• immune function

• cellular processes

This is where the internet often makes a leap.

A nutrient participating in a biological pathway does not automatically mean taking more of that nutrient improves every disease associated with that pathway.

That's an incredibly important distinction.

How much vitamin D do women need?

For most healthy adults ages 19–70, the U.S. Recommended Dietary Allowance is:

15 micrograms, or 600 IU, per day.

For adults over age 70:

20 micrograms, or 800 IU, per day.

The RDA during pregnancy and breastfeeding is also 600 IU per day.

These recommendations assume minimal sun exposure.

Individual medical needs can differ, particularly when someone has a documented deficiency or a condition affecting vitamin D absorption or metabolism.

Do women need more vitamin D during pregnancy?

Vitamin D remains important during pregnancy, particularly for maternal and fetal bone physiology.

The U.S. RDA during pregnancy is 600 IU daily.

But this doesn't mean every pregnant person should independently start high-dose vitamin D.

Prenatal supplementation should be considered alongside the rest of your nutrient intake, diet, medical history and laboratory findings when appropriate.

This is also why I care so much about preconception nutrition.

Preparing for pregnancy doesn't begin the day you see a positive pregnancy test.

Your nutritional status before conception matters too.

How do you know if your vitamin D is low?

The primary laboratory marker used to assess vitamin D status is serum 25-hydroxyvitamin D, often written as 25(OH)D.

But even here, there is nuance.

Different professional organizations have historically used somewhat different thresholds, and experts continue to debate what level should be considered “optimal” for every health outcome.

The NIH notes that levels of 20 ng/mL or higher are sufficient for most people under the Food and Nutrition Board framework, while levels below 12 ng/mL are associated with vitamin D deficiency.

That doesn't mean everyone needs to chase the highest number possible.

Should every woman get her vitamin D tested?

Not necessarily.

This is another place where wellness culture sometimes turns:

“This blood test exists.”

into:

“Everyone should get it.”

Those are different statements.

Routine screening of healthy people without a specific indication isn't universally recommended.

Testing may make more sense when someone has risk factors, symptoms, bone disease, malabsorption or another clinical reason their healthcare provider wants to evaluate vitamin D status.

More laboratory data doesn't automatically equal better healthcare.

Who is more likely to have low vitamin D?

Risk can be influenced by factors including:

• limited sun exposure

• conditions that impair fat absorption

• certain gastrointestinal disorders or surgeries

• kidney or liver disease

• dietary patterns low in vitamin D

• older age

• some medications

Skin pigmentation also affects cutaneous vitamin D production from sunlight.

But this is an area where we need nuance too.

Population differences in measured 25(OH)D don't necessarily translate perfectly into the same clinical outcomes across every racial and ethnic group.

Biology deserves more than a one-number-fits-everyone approach.

What foods contain vitamin D?

Vitamin D naturally occurs in relatively few foods.

Sources include:

• fatty fish such as salmon, trout and mackerel

• fish liver oils

• egg yolks

• some mushrooms, depending on UV exposure

Many foods are also fortified, including certain:

• milks

• plant-based milk alternatives

• cereals

• juices

Check the nutrition label because fortification varies.

Vitamin D2 vs. D3: what's the difference?

The two major supplemental forms are:

Vitamin D2 — ergocalciferol

and

Vitamin D3 — cholecalciferol

Both can raise vitamin D levels.

Vitamin D3 is commonly used in supplements and may raise serum 25(OH)D more effectively or for longer in some contexts, although the appropriate formulation depends on the individual.

And yes, vegan D3 exists—often derived from lichen or algae-based sources.

Does vitamin D “balance hormones”?

This is where I want women to be cautious.

Vitamin D participates in endocrine physiology, and researchers have studied associations between vitamin D status and numerous reproductive and metabolic conditions.

But that doesn't justify:

“Take vitamin D to balance your hormones.”

Which hormone?

What disorder?

What dose?

Was the person deficient?

Did supplementation improve an actual clinical outcome?

Those questions matter.

Low vitamin D may coexist with a condition without being the cause of that condition.

Association isn't causation.

What about vitamin D and PMOS/PCOS?

Vitamin D status has been studied extensively in people with PMOS, formerly called PCOS.

Researchers have explored possible relationships with metabolic markers, insulin resistance, reproductive function and other features of the syndrome.

Interesting?

Absolutely.

Proof that vitamin D supplements treat PMOS?

No.

PMOS is a complex polyendocrine, metabolic and ovarian syndrome.

No single vitamin corrects the condition.

If someone with PMOS is vitamin D deficient, addressing that deficiency may be appropriate for the same reason we'd address a deficiency in anyone else.

That's very different from selling vitamin D as a PMOS treatment.

Does vitamin D improve mood?

Low vitamin D levels have been associated with depression in observational research.

But randomized clinical trials have not consistently shown that vitamin D supplementation prevents depression or treats depressive symptoms.

That's the perfect example of:

Association ≠ intervention.

If your vitamin D is deficient, address it.

But depression deserves actual mental-health care—not a supplement bottle pretending to be one.

Can you take too much vitamin D?

Yes.

Vitamin D is fat-soluble, meaning excessive supplementation can accumulate.

Very high vitamin D intake can lead to hypercalcemia—too much calcium in the blood—which can cause serious health problems.

For adults, the general tolerable upper intake level is 4,000 IU per day, although healthcare professionals may prescribe higher doses temporarily when treating documented deficiency.

The upper limit isn't a target.

It means:

Don't assume more is better.

What about getting vitamin D from sunlight?

Your skin can synthesize vitamin D when exposed to UVB radiation.

But the amount produced varies significantly depending on:

• skin pigmentation

• latitude

• season

• time of day

• clothing

• sunscreen

• age

I don't recommend intentionally increasing unprotected UV exposure just to chase vitamin D.

Food and supplementation can provide vitamin D without adding unnecessary UV-related skin damage.

Should you take a vitamin D supplement?

Maybe.

Your decision should consider:

• dietary intake

• current supplements

• age

• pregnancy status

• sun exposure

• medical conditions

• medications

• laboratory findings when indicated

For some people, a multivitamin or prenatal already provides vitamin D.

Check your labels before stacking multiple products.

More isn't automatically better.

Frequently Asked Questions

How much vitamin D should a woman take every day?

The U.S. RDA for most adults ages 19–70 is 600 IU daily. Adults over 70 have an RDA of 800 IU. Individual needs may differ when deficiency or certain medical conditions are present.

What are the symptoms of vitamin D deficiency?

Mild deficiency may not cause obvious symptoms. Severe or prolonged deficiency can affect bone mineralization and contribute to bone pain or muscle weakness.

Is vitamin D3 better than D2?

Both forms can improve vitamin D status. D3 may raise serum 25(OH)D more effectively in some circumstances, but both are used clinically.

Should women take vitamin D for hormones?

Vitamin D is involved in numerous physiological systems, but it should not be marketed as a universal “hormone-balancing” supplement.

Is vitamin D important during pregnancy?

Yes. Vitamin D supports calcium metabolism and bone health during pregnancy. The U.S. RDA during pregnancy is 600 IU daily.

Can you take too much vitamin D?

Yes. Excessive vitamin D can cause toxicity and hypercalcemia. The general adult upper intake level is 4,000 IU daily unless higher doses are being used under medical supervision.

Giana's Take

Vitamin D is the perfect example of what happens when wellness takes a real piece of physiology and stretches it too far.

Vitamin D matters.

Bone health matters.

Deficiency matters.

Pregnancy nutrition matters.

But that doesn't mean vitamin D is the missing explanation behind every hormonal, fertility, mood or immune symptom.

As a biomedical engineer, I don't want women knowing less about supplements.

I want us knowing enough to ask:

What does this nutrient actually do?

How much do I need?

Am I deficient?

What does the evidence show?

And what is someone trying to sell me?

That's the difference between taking a supplement because TikTok told you to and making an informed decision about your health.

Your body deserves the second one.