I work from home. My desk is in the basement. During winter, I would go entire weeks without direct sunlight. I started feeling perpetually tired. Not sleepy — tired. The kind of bone-deep fatigue where getting off the couch felt like a major achievement.

My doctor tested my vitamin D levels. They were low. Not dangerously low, but low enough to explain why I felt like a phone at 8% battery all the time.

How much sun you actually need

Fifteen minutes of midday sun on your arms and face, three times a week, is enough for most people to produce adequate vitamin D. That’s it. Fifteen minutes. Not a beach day.

But that only works when the UV index is above 3. In much of the northern US, from November through February, the sun is too low in the sky to trigger vitamin D production, even at noon. You can stand outside all day and get nothing.

The food sources that help

You can’t get enough vitamin D from food alone — it’s just not concentrated enough. But these help:

• Fatty fish: Salmon, mackerel, sardines. A serving of salmon has about half your daily needs.
• Egg yolks: Not huge amounts, but every bit helps. Eat the whole egg.
• Fortified milk and orange juice: Check the label. Most milk in the US has vitamin D added.
• UV-exposed mushrooms: Some brands label this specifically. Regular mushrooms don’t have much.

The supplement reality

If you work indoors and live north of, say, Atlanta — you probably need a supplement at least during winter. The standard recommendation is 600-800 IU daily for adults. But many doctors recommend 1000-2000 IU, especially for people with low levels.

Vitamin D is fat-soluble, which means you need to take it with food that contains fat for it to absorb. Taking it with coffee on an empty stomach does almost nothing. Take it with breakfast.

The vitamin D3 form (cholecalciferol) is better absorbed than D2. The bottle will say which it is.

What changed for me

I started 2000 IU daily with breakfast. Took about three weeks to notice a difference. The fatigue didn’t vanish — but it lifted from “can’t function” to “normal tired.” I also started taking a ten-minute walk outside at lunch, no phone, no podcast, just walking. Even on cloudy days, I feel better for it.