The Truth About Vitamin D: Why Women Need More Than They Think

By: Holly L. Thacker, MD • Posted on November 03, 2026

Vitamin D is one of the most talked-about nutrients in women's health, yet it remains one of the most misunderstood. In fact, vitamin D is not truly a vitamin at all. It functions as a prohormone that plays critical roles throughout the body, influencing bone health, immune function, muscle strength, mood, and much more.

Why Vitamin D Matters

Vitamin D helps the body absorb calcium and phosphorus, making it essential for building and maintaining healthy bones. But its benefits extend far beyond the skeleton.

Research suggests that adequate vitamin D levels may support:

Immune system function
Muscle strength and fall prevention
Healthy blood pressure
Mood and emotional well-being
Oral health
Healthy pregnancy outcomes
Menstrual cycle regularity
Weight management efforts
Healthy aging

Low vitamin D levels have also been associated with higher risks of osteoporosis, certain cancers, diabetes, arthritis, multiple sclerosis, and respiratory infections.

Why So Many Women Are Low in Vitamin D

Many adults struggle to maintain optimal vitamin D levels, especially those who:

Live in northern climates
Spend most of their time indoors
Routinely use sunscreen
Have darker skin tones
Carry excess body fat
Are over age 40, when the skin becomes less efficient at producing vitamin D from sunlight

Even though sunlight is the body's natural source of vitamin D, geographical location, season, age, and lifestyle can significantly limit production. For many women, especially during winter months, sunlight exposure alone may not be enough.

What Is an Optimal Vitamin D Level?

There is often confusion about what constitutes a "normal" or "healthy" vitamin D level.

According to Dr. Holly Thacker, many laboratory reference ranges are based on population averages and may not reflect optimal health. While vitamin D levels above 30 ng/mL are generally considered adequate for bone health, many clinicians prefer levels of 50 to 60 ng/mL or higher to support immune function and overall health.

She notes that healthy individuals with substantial sun exposure, such as lifeguards during summer months, may naturally achieve levels well above 100 ng/mL.

As always, vitamin D targets should be individualized and discussed with your healthcare professional.

Vitamin D and Women's Health

Vitamin D has unique implications for women's health throughout the lifespan.

Adequate levels may help support:

Pregnancy

Vitamin D plays a role in fetal bone development, neurologic development, and reducing certain pregnancy complications.

Premenstrual Symptoms

Low vitamin D status has been associated with symptoms such as fatigue, mood changes, and menstrual discomfort.

Bone Health

Vitamin D remains a cornerstone of osteoporosis prevention because it helps the body absorb calcium effectively. However, calcium and vitamin D alone are not always enough to treat established osteoporosis.

Mood and Mental Health

Emerging research suggests vitamin D may play a role in supporting emotional well-being and reducing symptoms of depression in some individuals.

The Important Connection Between Vitamin D and Magnesium

One frequently overlooked aspect of vitamin D supplementation is magnesium.

Magnesium is required to activate and metabolize vitamin D. Without adequate magnesium, the body cannot efficiently convert vitamin D into its active form. In fact, taking vitamin D while magnesium deficient can further deplete magnesium stores.

Magnesium also helps support:

Bone health
Muscle function
Immune health
Mood regulation
Calcium balance throughout the body

Magnesium-Rich Foods

Good dietary sources include:

Spinach
Almonds
Cashews
Black beans
Avocados
Kale
Other leafy green vegetables

For women who need supplementation, several forms are available:

Magnesium glycinate: Often recommended for relaxation, sleep, and stress support.
Magnesium citrate: May help support bowel regularity.
Magnesium oxide: Commonly used for constipation relief.
Magnesium malate: Sometimes used for muscle support and energy.
Magnesium L-threonate: Marketed for brain health due to its ability to cross the blood-brain barrier.

Where to Get Vitamin D

Food Sources

While relatively few foods naturally contain significant amounts of vitamin D, some good sources include:

Salmon
Mackerel
Egg yolks
Fortified dairy products
Fortified plant milks
Fortified orange juice
Fortified cereals
UV-exposed mushrooms

Sun Exposure

Appropriate sunlight exposure can stimulate vitamin D production in the skin. However, effectiveness depends on age, skin pigmentation, season, geographic location, and the amount of exposed skin.

Supplementation

Many adults require vitamin D supplementation, particularly during winter months or when blood levels remain low despite dietary efforts. The amount needed varies greatly based on age, body weight, medical conditions, baseline vitamin D levels, and sun exposure.

Because vitamin D recommendations are highly individualized, discuss testing and supplementation with your healthcare professional before making significant changes to your regimen.

Vitamin D and Immune Health

Vitamin D has gained significant attention for its role in immune function. Immune cells contain vitamin D receptors, and vitamin D helps regulate immune responses. Studies have suggested that people with low vitamin D levels may experience worse outcomes from respiratory infections and may have increased susceptibility to illness.

Maintaining adequate vitamin D levels is one important component of supporting a healthy immune system year-round.

The Bottom Line

Vitamin D is far more than a bone-health nutrient. It influences immune function, muscle strength, mood, cardiovascular health, pregnancy outcomes, and overall well-being. Because many women are unable to maintain optimal levels through sunlight and diet alone, testing and individualized supplementation are often necessary. Just as importantly, maintaining adequate magnesium intake helps ensure vitamin D can be properly activated and utilized by the body.

By understanding the relationship between vitamin D, magnesium, nutrition, and lifestyle, women can take meaningful steps toward protecting their health and supporting healthy aging.

Be Strong, Be Healthy, Be in Charge!
-Holly L. Thacker, MD

About Holly L. Thacker, MD, FACP

Holly L. Thacker, MD, FACP is nationally known for her leadership in women’s health. She is the founder of the Cleveland Clinic Specialized Women’s Health Fellowship and is currently the Professor and Director of the Center for Specialized Women’s Health at Cleveland Clinic and Lerner College of Medicine at Case Western Reserve University. Her special interests are menopause and related medical problems including osteoporosis, hormone therapy, breast cancer risk assessment, menstrual disorders, female sexual dysfunction and interdisciplinary women’s health. Dr. Thacker is the Executive Director of Speaking of Women’s Health and the author of The Cleveland Clinic Guide to Menopause.

women's health, vitamins, supplements, vitamin D, magnesium, bone health

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