Vitamin D deficiency in the US and Canada: what the data actually shows
Government health survey data from both countries points the same direction — and winter makes it worse.
The US numbers, from NHANES
An analysis of National Health and Nutrition Examination Survey (NHANES) data from 2001 to 2018, covering over 70,000 participants, found 22.0% of the U.S. population had moderate vitamin D deficiency and 2.6% had severe deficiency — with another 40.9% classified as insufficient. Put together, well over half the population sampled wasn't in the sufficient range.
Who's most affected in the US data
The same NHANES analysis found deficiency rates were higher in women, in non-Hispanic Black Americans, in adults aged 20–29, and specifically during winter months — a consistent pattern across the dataset, not a one-off finding.
The Canadian numbers, from the Canadian Health Measures Survey
Statistics Canada's Canadian Health Measures Survey data from 2016–2019 found about 65% of Canadians had vitamin D levels above the 50 nmol/L threshold generally used to indicate adequacy — meaning roughly a third did not.
Why the Canadian gap widens sharply in winter
The seasonal swing is the more striking part of the Canadian data: in winter, close to 40% of Canadians fall below the 50 nmol/L threshold, compared to roughly 25% in summer. That's not a small seasonal dip — it's a near-doubling of the at-risk share of the population.
Why two large countries show the same pattern
Both datasets point to the same underlying mechanism: UVB synthesis of vitamin D in skin drops sharply at higher latitudes for several months a year, and most of the US and essentially all of Canada sit far enough north that winter sun simply can't produce meaningful vitamin D — see our deeper explainer on why Nordic-latitude winters are different.
What "insufficient" actually means for how you feel
Insufficiency isn't the same as a diagnosed deficiency requiring treatment — but the NHANES and Canadian data both link lower vitamin D status with the same nonspecific pattern: more reported fatigue, and a higher rate of low mood symptoms during winter months. None of this is proof of causation on its own; see our fuller, more hedged discussion in vitamin D3 benefits, explained.
Groups the data flags as higher-risk
Across both countries, the demographic pattern repeats: darker skin tones (which reduce UVB-driven synthesis), older adults, people who spend most daylight hours indoors, and anyone carrying more body fat (vitamin D is fat-soluble and stored in fat tissue) all show up as higher-risk groups in the underlying research.
Supplementation rates vs. deficiency rates — a gap worth noting
Despite these deficiency numbers, only a portion of at-risk adults in both countries report actually supplementing through the winter — a gap between documented need and reported behavior that shows up consistently in nutrition survey data, not a claim specific to any one country.
Testing is still the only way to know your own number
None of these population statistics tell you your individual status — a 25-hydroxyvitamin D blood test remains the only reliable way to know where you personally stand, regardless of what the national averages say.
What this means practically
If you live anywhere in the continental US or Canada, the population data alone is a reasonable prompt to think about winter vitamin D — not because you're guaranteed to be deficient, but because the base rates in both countries' own health survey data are high enough that it's a genuinely common, not rare, gap.
Frequently asked questions
Is vitamin D deficiency more common in Canada than the US?
The two datasets aren't directly comparable (different methodologies and cutoffs), but both show a similar pattern: a meaningful share of the population insufficient overall, with a sharp seasonal worsening in winter.
Does living further south in the US mean I don't need to worry about this?
Latitude matters, but it's not the only factor — indoor lifestyles, skin tone, sunscreen use and body composition all affect individual status regardless of which state or province you live in. The NHANES data includes plenty of deficient adults in southern states too.
What blood level counts as "deficient"?
Definitions vary slightly by health authority, but severe deficiency is generally set below 25–30 nmol/L, with insufficiency covering a wider range up to roughly 50 nmol/L — ask your doctor to interpret your specific test result rather than comparing it to a general cutoff.
Are these numbers getting better or worse over time?
The NHANES trend data from 2001–2018 shows a slight improvement — a small decrease in deficiency and a small increase in sufficiency — though the population-level gap remains substantial.
Do these statistics apply to children too?
Both surveys include younger age groups with somewhat different patterns; check your national health authority's specific pediatric guidance rather than applying adult cutoffs to children.
Should I get tested even without symptoms?
Given how common insufficiency is in both countries' own data, testing isn't unreasonable even without obvious symptoms — but it's a conversation for your doctor, not something this article can decide for you.
This article is for general information and isn’t medical advice. Talk to a healthcare professional before starting any new supplement, especially if pregnant, nursing, under 18, or managing a medical condition.
