Supplements for Cloudy, Rainy Climates: What the Research Says

November 12, 2026

If you live somewhere cloudy and rainy, vitamin D is the supplement with the strongest case, because your skin makes it from strong sunlight and the grey months don't supply much of it. Magnesium and omega-3 are the next two worth a look, mostly because many people come up short on them through food alone.

Why do cloudy climates leave you short on vitamin D?

Your skin makes vitamin D when UVB rays from the sun reach it. According to the NIH Office of Dietary Supplements, complete cloud cover cuts that UV energy by about half, and UVB doesn't pass through window glass, so a bright afternoon spent indoors doesn't count.

The season matters even more than the clouds. In a 1988 study, researchers found that winter sunlight in Boston (42°N) produced no vitamin D in skin from November through February, even on cloudless days. In Edmonton (52°N), that window ran from October through March. Seattle sits at about 47.6°N, right between the two.

Then add the clouds back in. NOAA climate data count about 226 heavily overcast days a year in Seattle and 222 in Portland, and in December through February roughly 70 of the 90 days are heavily overcast in both cities (NOAA data via Current Results). On the shortest day of the year, Seattle gets about 8 hours and 25 minutes of daylight. You can see month-by-month numbers for your city on the Grey Index.

How much vitamin D do adults need?

The NIH recommends 600 IU (15 mcg) a day for adults aged 19 to 70 and 800 IU (20 mcg) after 70, with an upper limit of 4,000 IU (100 mcg) a day. In the UK, the NHS advises that everyone should consider 10 mcg (400 IU) a day in autumn and winter, because between October and early March we don't make enough vitamin D from sunlight.

Those are general guidelines, and a simple blood test for 25-hydroxy vitamin D shows where you actually stand. It's worth talking to your doctor before you start, especially if you take any medications. Our Sunbreak softgel gives you 2,000 IU of vitamin D3 in one small daily dose, comfortably under the 4,000 IU upper limit.*

Does vitamin D help with winter mood?

The honest answer is that the research on vitamin D and seasonal mood is mixed, and a supplement isn't a treatment for seasonal depression. If your mood dips for weeks at a time every winter, talk to a doctor, because seasonal affective disorder is a real condition with its own proven treatments.

Which other nutrients are worth checking?

Magnesium comes up short for a lot of people. The NIH reports that 48% of Americans get less magnesium from food and drinks than they need. Adults need 310 to 420 mg a day depending on age and sex, and the upper limit for magnesium from supplements is 350 mg. Magnesium glycinate is the form known for being gentle on the stomach, and Calm Front gives you 275 mg of it per serving with dinner.*

Omega-3s come mostly from fatty fish such as salmon and sardines, so if you rarely eat fish, it's worth asking your doctor whether a supplement makes sense for you.

What does a simple grey-day routine look like?

A routine that works in the dark months is built around three small habits.

Morning: take your vitamin D with breakfast. It's fat-soluble, so many people pair it with a meal. Then get outside for a walk in the first hours of daylight, even when it's cloudy.
Afternoon: step outside again if you can while there's still daylight, which in December can be gone before 4:30.
Evening: take magnesium glycinate with dinner and let the evening slow down.

If you'd like the morning part done for you, The Morning Set puts Sunbreak, Greenhouse and Bright Spell together in one box. For more on the morning side, read Vitamin D in Pacific Northwest winters.

Frequently asked questions

Can I get vitamin D through a window?

No. UVB rays don't pass through glass, so sitting by a sunny window won't help your skin make vitamin D.

Do I need vitamin D in summer too?

The NHS says most people can make enough from sunlight between late March or early April and the end of September. People who are rarely outdoors may need it all year.

How much vitamin D is too much?

Both the NIH and the NHS set the adult upper limit at 4,000 IU (100 mcg) a day, unless your doctor advises otherwise.

Is Seattle the cloudiest city in the US?

It depends on how you count. NOAA data put Seattle first for heavily overcast days, at 226 a year, while Buffalo has the most days with any cloud, at 311. Read more in What Is the Cloudiest City in the US?

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.