In a Seattle or Portland winter, your skin makes little or no vitamin D from sunlight. Seattle sits at 47°N, and research at nearby latitudes found the sun too weak for skin to make vitamin D for roughly four to six months of the year. That leaves food and supplements to do most of the work until spring.
Why can't the winter sun make vitamin D?
Skin makes vitamin D from UVB light. In winter the sun sits low, and UVB is filtered out before it reaches the ground. A study in Boston (42°N) found skin made no vitamin D from sunlight from November through February. At 52°N, the gap ran from October through March (Webb, Kline and Holick, 1988). Seattle and Portland sit between the two. Clouds, shorter days and time spent indoors cut it further.
How grey is a Northwest winter?
Seattle averages 226 cloudy days a year and about 53 hours of sunshine in December. Phoenix gets 245 December hours. See every city in the Grey Index.
How much vitamin D per day do you need?
Most adults need 600 IU (15 mcg) of vitamin D a day, and adults over 70 need 800 IU (20 mcg). That is the US recommended amount from the NIH Office of Dietary Supplements, and it counts vitamin D from food, drinks and supplements together. In the UK, the NHS advises everyone to consider 10 mcg (400 IU) a day from October to March (NHS).
| Life stage | Recommended a day | Upper limit a day |
|---|---|---|
| Babies, birth to 12 months | 400 IU (10 mcg) | 1,000 IU to 6 months, 1,500 IU from 7 months |
| Children 1 to 13 | 600 IU (15 mcg) | 2,500 IU (ages 1 to 3), 3,000 IU (4 to 8), 4,000 IU (9 to 13) |
| Teens 14 to 18 | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| Adults 19 to 70 | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| Adults 71 and older | 800 IU (20 mcg) | 4,000 IU (100 mcg) |
| Pregnant or breastfeeding | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
Source: NIH Office of Dietary Supplements. Needs vary from person to person. A simple blood test for 25-hydroxyvitamin D shows your level, and the NIH says 20 ng/mL (50 nmol/L) or above is adequate for most people. Ask your doctor what is right for you. For the wider picture, see our guide to supplements for cloudy, rainy climates.
How much vitamin D is too much?
For adults, the upper limit is 4,000 IU (100 mcg) a day from all sources, unless a doctor advises more for a set time. Very high blood levels can cause nausea, vomiting, muscle weakness, confusion, dehydration and kidney stones, according to the NIH Office of Dietary Supplements. Levels that high almost always come from taking too much in supplements. You can't get too much vitamin D from the sun, because your skin limits how much it makes.
Where can you get vitamin D in winter?
Few foods contain much of it. The best are fatty fish such as salmon and trout, plus fortified milk, plant milks and cereals. Egg yolks and some mushrooms add a little. Many people in grey climates also choose a supplement through the darker months.
Does vitamin D help with winter mood?
Research on vitamin D and seasonal mood is mixed, and vitamin D is not a treatment for seasonal affective disorder. If winter low mood is affecting your daily life, talk to a doctor.
FAQ
Can I get enough vitamin D from a sunny winter day?
At Northwest latitudes, research suggests not between roughly November and February, even in clear weather.
How much vitamin D should I take in winter?
Most adults need 600 IU a day, or 800 IU over 70. In a Northwest winter most of that has to come from food or a supplement. Your doctor can check your level and tell you whether you need more.
Is 2,000 IU of vitamin D a day too much?
For most adults, no. 2,000 IU is half the 4,000 IU daily upper limit the NIH sets for adults, counting food and supplements together. Check with your doctor if you take other products with vitamin D or have a health condition.
Is D3 or D2 better?
Both raise vitamin D levels. Some research suggests D3 raises and keeps levels higher for longer (NIH ODS).
How much vitamin D is too much?
For adults, more than 4,000 IU (100 mcg) a day from food and supplements together, unless a doctor advises otherwise.
Ray™'s take: You can't change the forecast. You can plan for it. Our morning lineup starts with Sunbreak, 2,000 IU of vitamin D3 in one small softgel.
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. This article is for education and is not medical advice.