Why is vitamin D deficiency so common in Wisconsin?

From roughly October through April, the sun's angle in Wisconsin is too low for the skin to produce meaningful amounts of vitamin D — even on sunny days. Add cloud cover, cold-driven indoor time, and full-coverage winter clothing, and most Wisconsin residents enter spring with low or borderline vitamin D levels.

What blood level counts as deficient?

Vitamin D is measured as 25-hydroxyvitamin D (25-OH D). Most labs flag <20 ng/mL as deficient and 20–29 ng/mL as insufficient. Many clinicians, including in mental health practice, target a range of 40–60 ng/mL for optimal mood, immune, and bone health.

Can low vitamin D cause depression or anxiety?

The relationship is correlational rather than purely causal, but multiple studies link low vitamin D status with higher rates of depression, fatigue, and anxiety symptoms. Correcting deficiency is a reasonable supportive measure alongside evidence-based treatment — not a replacement for it.

How much vitamin D should I take?

Dosing should be individualized based on a 25-OH D blood test, body weight, and other factors. Typical replacement doses range from 1,000–5,000 IU/day of vitamin D3, with periodic recheck. Higher prescription doses are sometimes used short-term for severe deficiency. Don't supplement at high doses without testing.

Wisconsin Health

Vitamin D Deficiency and Wisconsin Winters: What Every Patient Should Know

Q: Can low vitamin D cause depression or anxiety?

The relationship is correlational rather than purely causal, but multiple studies link low vitamin D status with higher rates of depression, fatigue, and anxiety symptoms. Correcting deficiency is a reasonable supportive measure alongside evidence-based treatment — not a replacement for it.

Q: How much vitamin D should I take?

Dosing should be individualized based on a 25-OH D blood test, body weight, and other factors. Typical replacement doses range from 1,000–5,000 IU/day of vitamin D3, with periodic recheck. Higher prescription doses are sometimes used short-term for severe deficiency. Don't supplement at high doses without testing.

Q: Can a Wisconsin telehealth provider order vitamin D testing?

Yes. Inspiring Transformations LLC can order labs at a local Wisconsin draw site, review results virtually, and individualize a supplementation and monitoring plan — all without an in-person visit.

From October through April, Wisconsin sunlight isn't strong enough to produce meaningful vitamin D — and your mood, energy, and immune system feel it.

Christine M. Forge, MSN, PMHNP-BC, FNP-C• 10 min read•May 2026

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Vitamin D isn't really a vitamin — it's a hormone. The skin produces it when UVB rays from the sun strike at a steep enough angle. North of about 35° latitude, that angle disappears for roughly half the year. Wisconsin sits at 42–47°N, which means most patients lose the ability to make vitamin D entirely from October through April.

The result: Wisconsin residents enter spring with some of the highest rates of vitamin D insufficiency in the country — affecting bone health, immune function, mood, and energy.

Key Takeaways

Wisconsin's latitude makes winter vitamin D production essentially zero from October through April.
Test 25-OH vitamin D — don't supplement blindly at high doses.
Levels of 30–60 ng/mL are commonly targeted; 40–60 ng/mL is often optimal for mood and immunity.
Low vitamin D is correlated with depression, fatigue, and frequent illness — though it's not a standalone cause or cure.
Telehealth providers can order labs and individualize supplementation across Wisconsin.

Why Wisconsin Winters Are a Vitamin D Black Hole

Sun angle is too low

Above ~35° latitude, the winter sun is too low in the sky for UVB rays to penetrate the atmosphere. Wisconsin sits well above that threshold — meaning the skin can't make vitamin D, even on a clear day.

Cloud cover & lake-effect weather

Wisconsin winters average more cloudy days than most of the lower 48. Even when sun angle improves in early spring, ambient UVB exposure stays low.

Indoor time and clothing

Cold-weather clothing covers most of the skin. Combined with months of indoor heating, dietary intake becomes the only real source of vitamin D for half the year — and most diets fall short.

Symptoms of Low Vitamin D

Persistent fatigue and low energy
Low or depressed mood
Muscle aches, weakness, or bone pain
Frequent colds, flu, or respiratory illness
Hair thinning or shedding
Slow wound healing
Worsened sleep quality

These symptoms overlap heavily with depression, anemia, and thyroid disease — which is why testing matters before attributing symptoms to a single cause.

Testing & Supplementation

Test First

A simple 25-hydroxyvitamin D blood test gives a clear picture of status. Most Wisconsin patients benefit from testing once in late winter (lowest point) and again after 3–4 months of supplementation.

Supplement Smartly

Vitamin D3 (cholecalciferol) is generally preferred over D2. Typical maintenance is 1,000–2,000 IU/day; replacement doses for documented deficiency are higher and should be individualized with a clinician.

Vitamin D and Mental Health

Vitamin D receptors are found throughout the brain, including areas involved in mood regulation. Multiple observational studies link low vitamin D status to higher rates of depression, anxiety, and seasonal mood changes — though causality is still being clarified.

In Wisconsin telehealth practice, vitamin D testing is typically part of a broader workup for fatigue, depression, or seasonal mood symptoms. Correcting deficiency is a reasonable supportive intervention — but it's not a substitute for evidence-based psychiatric treatment when SAD or major depression is present.

Frequently Asked Questions

Wisconsin Telehealth Lab Workups

Inspiring Transformations LLC can order vitamin D and related labs at a local Wisconsin draw site, review results virtually, and individualize a supplementation and monitoring plan.

Wisconsin Telehealth Book Appointment

Medical Disclaimer: This article is for educational purposes only and is not a substitute for individualized medical advice, diagnosis, or treatment. Do not start high-dose vitamin D supplementation without testing and clinical guidance.

References

Holick, M. F. Vitamin D deficiency. New England Journal of Medicine.
Endocrine Society Clinical Practice Guideline: Evaluation, Treatment, and Prevention of Vitamin D Deficiency.
Anglin, R. E. S., et al. Vitamin D deficiency and depression in adults: systematic review and meta-analysis. British Journal of Psychiatry.
National Institutes of Health Office of Dietary Supplements. Vitamin D Fact Sheet.

Virtual Healthcare

Psychiatric Mental Health Nurse Practitioner & Family Nurse Practitioner

Christine provides telehealth psychiatric and primary care to patients across Wisconsin, Florida, and Nevada.