Vitamin D in a Wisconsin Winter: Why So Many of Us Run Low, and What To Do About It

There is a stretch of every Wisconsin year, roughly from late fall to early spring, when the sun over Green Bay is too weak for your skin to make vitamin D, no matter how clear and cold and beautiful the day looks. Your body runs on what you stored up in summer, plus what you eat and supplement. By February, a lot of those stores are empty.

This is not a fringe problem. According to Examine.com, vitamin D insufficiency (a blood level at or below 20 ng/mL) may affect as much as 50 percent of people worldwide, including 41.6 percent of Americans. In other words, if you live in northeast Wisconsin and have never thought about vitamin D, you are the exact person this article is for.

Why Green Bay is a special case

Vitamin D is the rare vitamin your body manufactures itself, in your skin, when sunlight hits it. That system works beautifully at our latitude in July. In January, the sun's angle is so low that the UVB rays needed for the job mostly never reach you. Add indoor work, long sleeves from October to April, and sunscreen in the months when you are outside, and the math gets difficult. Darker skin needs even more sun exposure to make the same amount, and insufficiency rates are highest in Black and Hispanic Americans.

Should you test, or just supplement?

The only way to know your level for sure is a blood test called 25-hydroxyvitamin D. Examine notes that testing is not routine for the general public, and that in many cases a sensible supplement dose is chosen based on risk factors alone. Our honest advice in the store:

• Ask your doctor for the test at your next physical, especially if you are over 50, rarely get midday sun, have darker skin, or have bone health on your mind. Knowing your number turns guesswork into a plan.
• If you do not test, a typical adult dose in the research is 800 to 2,000 IU a day, which is a reasonable, conservative place to be through the winter.

D3 or D2?

Pick D3 (cholecalciferol). Examine's review is clear that D3 is generally recommended over D2 (ergocalciferol) because D3 raises blood levels more effectively. Taking it with a meal that contains some fat is the traditional advice for absorption.

What vitamin D actually does, honestly graded

What supplementation reliably does, per Examine: it raises your blood vitamin D level (large effect, which sounds obvious, but it confirms the dose reaches the target), and it is associated with small improvements in bone mineral density and fall risk, and moderate improvements in asthma symptoms in the studies reviewed.

What it does not do, despite years of headlines: in Examine's grading, vitamin D supplementation showed no effect on fracture risk, on catching upper respiratory infections, on major cardiac events, on weight loss, or on testosterone. Vitamin D is a genuine essential, and being low is worth fixing. It is not a force field.

The ceiling matters

Vitamin D is fat soluble, so unlike vitamin C, the extra does not just wash out. The tolerable upper intake level for adults is 4,000 IU (100 mcg) a day, including in pregnancy. Do not go above that unless a healthcare professional who knows your labs advises it and monitors you, because excess vitamin D raises blood calcium, and that is where the real trouble starts. Be extra careful if you take digoxin, calcium channel blockers, or thiazide diuretics, or if you have kidney disease, and check with your pharmacist.

A simple Green Bay winter plan

1. Decide test or no test with your doctor, and write the number down if you get one.
2. Choose a D3 you will actually take every day, somewhere in the 800 to 2,000 IU range for most adults.
3. Take it with food, keep it with your breakfast things, and give it the whole season, not two weeks.
4. Revisit in spring. Your needs in June are not your needs in January.

The bottom line

At this latitude, low vitamin D is the default, not the exception. The fix is inexpensive and well understood: know your risk, take a sensible D3 dose through the dark months, and respect the ceiling. If you want help picking a strength or a form (drops, softgels, or a D3 with K2 combination), bring your questions into B-Alive in Green Bay or De Pere. Thirty-seven winters of doing this is kind of our thing.

This article is general education, not medical advice. Talk with your healthcare professional about what is right for you.