In summer, a little time outdoors lets your skin make vitamin D. In winter, for much of the country, that switch basically turns off. Here's what that means for your vitamin D, and a sensible way to handle the darker months.
Written by Vita Globe Editorial Team | Reviewed against NIH guidance, the 2024 Endocrine Society guideline and peer-reviewed research
Do you need more vitamin D in winter?
Often, yes, if you live in the northern half of the U.S. A classic study found that winter sunlight in Boston (about 42°N) didn't produce vitamin D in skin from November through February[1]. Because few foods contain much vitamin D, many people rely on a supplement in winter. The RDA stays the same year-round, at 600 to 800 IU a day, with an adult upper limit of 4,000 IU[2].
Caveat: "More in winter" means making up for lost sun, not megadosing. Your daily total should still stay within the upper limit unless your doctor says otherwise.
Sources: Webb et al., JCEM 1988 · NIH ODS · Endocrine Society 2024 · Verified 2026-09-27
IN THIS ARTICLE
Why does vitamin D drop in winter?
Your skin makes vitamin D when it's hit by UVB rays. In winter, the sun sits lower in the sky, so UVB has to travel through more atmosphere and much less reaches the ground. Add shorter days, more time indoors and more clothing, and skin production drops sharply[2].
The effect depends a lot on where you live. In a well-known study, researchers exposed a vitamin D precursor to sunlight in different cities. In Boston, winter sunlight didn't produce vitamin D from November through February. In Edmonton, Canada, further north, the "vitamin D winter" ran from October through March. Further south, sunlight still produced some vitamin D in midwinter[1].
Roughly speaking, the further north you live, the longer your "vitamin D winter" lasts, and the less winter sun alone does for your vitamin D.
Who is most likely to run low in winter?
The NIH lists several groups at higher risk of low vitamin D year-round, and winter makes each of them more likely to fall short[2]:
- People with darker skin, since more melanin reduces vitamin D production from sunlight
- Older adults, whose skin makes vitamin D less efficiently
- People who spend most of their time indoors or cover most of their skin
- People with obesity
- People with conditions that limit fat absorption, such as Crohn's or celiac disease
We cover these in more detail in vitamin D deficiency signs, causes and treatment.
How much vitamin D should you take in winter?
The official requirement doesn't change by season. The RDA is 600 IU a day for ages 1 to 70 and 800 IU after 70, and those numbers already assume minimal sun exposure[2]. Because the RDA was set with little or no sun in mind, winter is exactly the scenario it's designed for.
In practice, many adults choose 1,000 to 2,000 IU a day through the colder months, which stays well below the 4,000 IU upper limit[2]. The 2024 Endocrine Society guideline suggests extra vitamin D above standard intake for children and teens, adults 75 and older, pregnant people and adults with high-risk prediabetes, and doesn't recommend routine testing for other healthy adults[3].
For a side-by-side of common doses, see How much vitamin D3 per day?.
Does vitamin D help with winter colds?
This is the question most people are really asking. The best evidence is a meta-analysis of individual data from 25 randomized trials, which found vitamin D modestly reduced the risk of acute respiratory infections overall. The effect was largest in people who were very deficient, and daily or weekly dosing worked better than big one-off doses[4].
So it's reasonable to see vitamin D as part of a winter routine if you tend to run low. It's not a force field. We compare vitamin D with vitamin C and zinc in our look at vitamin C, zinc and vitamin D for colds.
The honest summary
- In the northern U.S., winter sun doesn't make meaningful vitamin D[1].
- The RDA doesn't change, but getting it from food alone is hard, so a supplement often fills the gap[2].
- Vitamin D may modestly lower respiratory infection risk, mostly in people who were low[4].
What about the winter blues?
Low mood in winter is common, and vitamin D often gets suggested as a fix. The research is mixed at best, with large prevention trials finding no benefit. We cover it honestly in vitamin D and mood. If your mood changes are significant, talk to a doctor. Seasonal affective disorder has established treatment options, including light therapy, psychotherapy and medication[5].
Our option
Vita Globe Vitamin D3 2,000 IU Gummies
Each 2-gummy serving provides 2,000 IU (50 mcg) of vitamin D3 in a strawberry-flavored gummy that's vegan, gluten-free and non-GMO, and tested by an independent third-party lab. A simple way to cover the months when your skin isn't making much vitamin D, while staying at half the adult upper limit.
Our option
Vita Globe Zinc Citrate Gummies with Vitamin D & Echinacea – Pouch
Prefer one pouch for the cold-weather months? Each 2-gummy serving provides 50 mg of zinc (as zinc citrate), 50 mcg (2,000 IU) of vitamin D and 4 mg of echinacea extract in a mixed-berry gummy. Because it already contains vitamin D, choose it instead of a standalone D3, not in addition to one.
Frequently asked questions
Should I take vitamin D in winter only?
You can, if you get regular sun the rest of the year. Many people take it year-round because indoor lifestyles limit sun even in summer[2].
Can you get vitamin D from the sun in winter?
In much of the northern U.S., very little or none. Boston sunlight didn't produce vitamin D from November through February in one study[1].
When should I start taking vitamin D for winter?
Many people start in fall, as days shorten. Vitamin D levels build gradually over weeks[2].
Does a sunny winter day help?
It depends on latitude. In northern cities, even bright winter sunlight contains too little UVB for your skin to make vitamin D[1].
Does vitamin D prevent winter colds?
It may modestly lower the risk, especially if you're deficient[4]. It isn't a guarantee.
Sources
- Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988;67(2):373-378. doi:10.1210/jcem-67-2-373
- Office of Dietary Supplements, National Institutes of Health. Vitamin D: Fact Sheet for Health Professionals. Accessed September 27, 2026. ods.od.nih.gov/factsheets/VitaminD-HealthProfessional
- Demay MB, Pittas AG, Bikle DD, et al. Vitamin D for the prevention of disease: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2024;109(8):1907-1947. doi:10.1210/clinem/dgae290
- Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017;356:i6583. doi:10.1136/bmj.i6583
- National Institute of Mental Health. Seasonal Affective Disorder. Accessed September 27, 2026. nimh.nih.gov
About the Vita Globe Editorial Team
The Vita Globe Editorial Team researches and writes our wellness content, working from peer-reviewed research, systematic reviews and guidance from bodies such as the NIH and the FDA. We cite our sources inline and update articles when the evidence changes.
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 informational purposes only and is not a substitute for medical advice. Talk to your healthcare provider before starting any new supplement, particularly if you are pregnant, nursing, taking medication, or caring for a child.
