Vitamin D deficiency doesn’t always feel dramatic.
Sometimes it’s just a heavier brain, slower recall, or sleep that doesn’t leave you rested —classic vitamin D deficiency symptoms I ignored for years.
That’s what I started noticing each winter. And year after year, blood tests confirmed it—my levels kept dipping below 40 nmol/L. One even came back at 31.
I wasn’t doing nothing. I was supplementing, getting outside when I could, and following general advice.
But, it wasn’t enough.
So I stopped relying on assumptions and started testing.
Over the past few winters, I’ve focused on dialing in the right dose and frequency—and tracking how it impacts my levels.
As you’ve probably heard me mention, vitamin D does more than regulate calcium or prevent rickets. It’s deeply involved in mood, memory, and how the brain adapts over time—critical factors in staying sharp and avoiding the shrinking that often comes with age.
In this post, I’ll walk you through what I’ve learned:
- What my numbers looked like through multiple winters
- The mistakes that kept me low
- And the vitamin D protocol that’s finally keeping me in range
If you want the science behind how vitamin D supports brain health and aging, you’ll find that in the full guide on vitamin D and cognitive aging.
But if you’re here for the practical blueprint, let’s get started.
Table of Contents
How Common Is Vitamin D Deficiency—Really?
Plenty of people assume that living in a sunny place means they’re covered.
Places like California, Florida, or southern Europe seem like safe bets for natural vitamin D.
And in tropical regions like India or the Middle East, where sunshine is year-round, deficiency should be rare—right?
Not even close.
A global analysis of 7.9 million participants across 81 countries found vitamin D deficiency prevvalence to be the following:
- ~ 16% had severe deficiency (<30 nmol/L)
- ~ 50% had moderate deficiency (<50 nmol/L)
- And a staggering >76% had levels below 75 nmol/L—considered by many experts to be the threshold for sufficiency.
Even in the United States, which has widespread food fortification and supplement use:
Weighted prevalence of serum 25(OH)D <25, 25–50, 50–75, and >75 nmol/L in Americans ages >1 year between 2001 and 2018 by ethnicity.
- ~ 25% of Americans had levels below 50 nmol/L
- > 40% fell into the “insufficient” 50–75 nmol/L range
- ~ 34% had levels > 75 nmol/L
About one-third of Americans had levels above 75 nmol/L, though the study doesn’t say how far above. It’s a reminder that overshooting can sometimes be just as unhelpful as falling short.
Meanwhile, in places with year-round sun like India, vitamin D deficiency prevalence is even more widespread.
Based on where you draw the line—moderate or severe vitamin D deficiency—58% to 81% of adults fall below the recommended levels.
Cultural habits—like limited skin exposure or avoiding the heat—make a bigger difference than latitude alone.
“Year-round sun doesn’t guarantee adequate vitamin D when people spend most of their time indoors or avoid direct exposure,” one study noted.
Vitamin D Deficiency Prevalence of individuals from urban Bangalore (middle aged and above without dementia)
[Red square] Normal (> 30 ng/ml).
[Blue square] Deficient (< 20 ng/ml).
[Yellow square] Insufficient (21–29 ng/ml).
Whether you live in Los Angeles, Helsinki, or Chennai—if you’re not testing, you really don’t know where you stand.
My Early Winter Strategy (Back in 2019)
Back in 2019, when I first started tracking my vitamin D levels in winter, I realized I’d been making vague assumptions.
I live far from the tropics, and from October to April, sunlight just doesn’t cut it. Add in minimal intake from food, and my levels dipped—year after year. One test landed at 35 nmol/L.
At the time, I figured a small daily supplement would be enough. I wasn’t measuring inputs. I wasn’t testing mid-season. I just increased my dose “a bit” and hoped it would carry me through.
That’s when I started asking better questions:
- How much Vitamin D3 should I take daily?
- How much vitamin D do I actually store from the summer?
- How fast does it deplete?
- And what’s the minimum I need to avoid that late-winter drop?
- And what’s the maximum I before I exceed my target level?
What I Found
- 1,000 IU per day raises blood levels by around 25 nmol/L over several weeks
- The body stores vitamin D as calcidiol in both blood and fat—but that storage varies a lot
- How much sunlight for vitamin D varies widely, but the literature seems to suggest that 15 minutes of sun can generate ~1,000 IU, but only if UVB is strong enough (it’s not, where I live, in winter)
- And long-term high doses—2,000 to 10,000 IU daily—may be too much for some people
I didn’t realize how much sunlight is needed for vitamin D in winter, especially at my latitude.
My Initial Vitamin D Protocol
I started with a banking strategy: Maybe I can “bank” extra vitamin D in summer—then coast through winter.
Here’s how it looked:
- 15 minutes per day × 60 days = ~60,000 IU stored
- Divide that across the winter? That gives about 75 days at ~800 IU/day
- But with vitamin D’s half-life, even that buffer drops off fast
The takeaway was clear: even with summer sun, I couldn’t count on reserves to carry me through.
So I started taking 1,000 IU daily, beginning in mid-fall.
It was a simple shift, but one that made testing and refining possible.
Arriving at Vitamin D Protocol v.2
By early 2023, I’d been supplementing regularly for a few winters—but my levels still dropped to 31 nmol/L. That’s well into the zone where severe vitamin D deficiency symptoms can start to show.
That’s when I realized: taking vitamin D wasn’t the issue. I needed to fine-tune how much, how often, and season—based on my test results.
I adjusted the plan.
For a few months, I tried 5,000 IU, taken 3–4 times per week.
My levels jumped to 150 nmol/L, significantly above my personal target range.
From there, I started scaling back—testing, retesting, and watching the trends. What eventually worked was simple:
- 2,000–3,000 IU, 3 to 4 days per week
- Natural sun exposure in summer
- Routine testing to make small corrections
This approach held my levels between 58 and 84 nmol/L, which sits comfortably within my year-round personal target of 60–85 nmol/L.
The Chart That Told the Story: A Clearer Pattern
The chart below shows how things shifted—
From seasonal dips to overshooting, and finally to something more stable.
My Current Vitamin D Strategy
Most people ask: how much vitamin D3 should I take daily?
After several years of tracking and adjusting, this is the vitamin D protocol that’s currently working best:
I Start Early Now
I don’t wait until October anymore. These days, I begin supplementing in late August or early September. The sun is still strong, but by then my levels are already tapering.
Starting a couple weeks before the drop just makes more sense now.
5,000 IU Was Too Much—For Me
That short experiment with 5,000 IU several times a week shot my levels to 150 nmol/L.
Technically not toxic, but well above my target end range. It didn’t feel like a stable solution—and the crash down to 58 nmol/L after I stopped confirmed it.
That experience reinforced a key insight: smaller, consistent doses are more effective for maintaining balance than large, intermittent ones.
That said, 5,000 IU could be the right dose for you.
I Use Seasonal Checkpoints
I test my levels a few times a year—late winter, midsummer, and sometimes in the fall, depending on my routine.
That’s usually enough to spot trends and adjust as needed.
My Protocol—Right Now
- 2,000–3,000 IU, 3 to 4 days per week (depending on how much sun I get that day/week)
- I still aim for midday sun in the summer
- No meaningful intake from food or fortification—those are incidental
We’ve since included this chart and testing pattern in our private Longevity Vault materials, since it illustrates how seasonal patterns can be smoothed with small, consistent shifts.
What Are Optimal Vitamin D Levels?
While normal vitamin D levels by age can vary, I aim to stay between what I consider to the optimal vitamin D levels of 60 and 85 nmol/L—slightly above the standard RDA threshold. For me, that range tends to support better sleep, steadier energy, and clearer thinking through the darker months.
I also avoid pushing too far above 100 nmol/L, since excessively high levels have been linked to diminishing returns—and, in some studies, potential cognitive risks.
FAQ – My Answers After Years of Tracking
What are optimal vitamin D levels?
Functional medicine often defines optimal vitamin D levels as 100–150 nmol.
Personally, I aim for a slightly lower but still proactive range: 60–85 nmol/L. That’s where I’ve noticed the biggest benefits—steadier energy, better sleep, and clearer thinking, especially in winter.
I also avoid going much above 100 nmol/L, since some research suggests diminishing returns and links to cognitive risks at higher levels.
How much vitamin D3 should I take daily? Is 1,000 IU per day enough?
It might be—for some. But based on my own tracking, 1,000 IU/day wasn’t enough to keep me above 65 nmol/L in late winter. For me, the sweet spot ended up being 2,000–3,000 IU, 3–4 days/week.
Can I rely on summer sun alone?
Depends on where you are, your skin tone, your genetics and how much sun you get, as how much sunlight for vitamin D varies per person.
For me, not really. I used to assume my July/August sun exposure would cover the winter. But vitamin D made from sunlight drops off quickly—serum levels start falling within weeks, and body fat stores only stretch so far. Even with good summer sun, I still landed at 31 nmol/L by spring.
How do you avoid vitamin D toxicity?
By not megadosing long-term, and testing regularly.
Toxicity typically shows up at sustained intakes above 10,000 IU/day, but some people may reach unsafe levels even on 2,000–5,000 IU, while some people may need 5,000 IU.
The safest way to stay in range is to supplement modestly and to adjust dosage by testing a few times a year.
Do I need 50,000 IU prescription doses?
Not necessarily—especially if you don’t have malabsorption or a diagnosed deficiency. I’ve personally done better with smaller, consistent daily or weekly doses instead of high-dose prescriptions.
That said, it’s a good idea to test if you have genes that affect vitamin D synthesis—unless your doctor has a specific reason for prescribing it. I used this test to check mine before deciding on a long-term approach.
Always talk to your provider if you have clinical vitamin D deficiency or gut absorption issues.
How much vitamin D3 should I take daily in winter?
There’s no one-size-fits-all answer.
For me, 2,000–3,000 IU a few days a week is enough. That might sound low to some, but I’ve seen it hold me between 65–85 nmol/L during the winter months. Your needs may differ—especially depending on skin tone, body weight, latitude, and how much sun you’re actually getting.
How much vitamin D can your body actually store?
There’s no universal number—it depends on factors like body fat, skin tone, and sun exposure. Estimates range from 10,000 to 50,000 IU, mostly stored as 25(OH)D (calcidiol) in fat tissue. But even at the high end, it’s not enough to cover a whole winter without supplementation. Storage helps—but it’s not a full strategy.
What are vitamin D deficiency symptoms in adults?
Fatigue, poor sleep, and brain fog are some of the most common vitamin D deficiency symptoms. For me, it showed up as low energy and slow recall.
How to increase vitamin D levels safely?
Small, consistent doses + testing. Avoid megadosing long-term. Summer sun helps but isn’t enough alone.
How can I avoid deficiency altogether?
You can’t wing it.
My answer: test regularly, track your winter trends, and create a personalized strategy. Then you can decrease the frequency of testing.
Don’t rely on assumptions about sunshine or diet.
Solving Vitamin D Deficiency: Practical Tips From 5 Years of Testing
Vitamin D deficiency wasn’t something I expected. I was active, mostly healthy, and already supplementing. And yet—my levels dropped to 31 nmol/L.
That’s what finally pushed me to stop relying on general advice and start paying attention to my own data.
What I’ve learned since is this:
- Deficiency is common, even in sunny regions
- It’s not just about sun exposure—it’s about timing, genetics, and habit
- And it took less than I thought to drift out of range
Beyond brain health, low vitamin D has been linked to other long-term risks—including abnormal lipid profiles, as shown in the chart below.
Table 3 Percentage of individuals with abnormal lipid levels across the three levels of vitamin D.
The key to hitting optimal vitamin D levels wasn’t intensity. It was rhythm, testing, and seasonal timing. I tested seasonally, adjusted as needed, and stuck to a dose that matched my data.
If you’re navigating this yourself:
- Start by checking your baseline. Home test kits or a simple blood draw is enough.
- If you want the full science behind why this matters—especially for brain health and cognitive aging—you’ll find it all in my vitamin D for neuroplasticity & brain health deep-dive.
- And if you want to follow along with future results, adjustments, or protocols, I share it all in the newsletter.
Aging well doesn’t require perfect control.
But it does reward attention.
References
- Ghosh, A., S, M., Sunny, A.S. et al. Prevalence and patterns of vitamin D deficiency and its role in cognitive functioning in a cohort from South India. Sci Rep 14, 11215 (2024). https://doi.org/10.1038/s41598-024-62010-5
- Cui A, Zhang T, Xiao P, Fan Z, Wang H, Zhuang Y. Global and regional prevalence of vitamin D deficiency in population-based studies from 2000 to 2022: A pooled analysis of 7.9 million participants. Front Nutr. 2023 Mar 17;10:1070808. doi: 10.3389/fnut.2023.1070808. PMID: 37006940; PMCID: PMC10064807.
- Cui A, Xiao P, Ma Y, Fan Z, Zhou F, Zheng J, Zhang L. Prevalence, trend, and predictor analyses of vitamin D deficiency in the US population, 2001-2018. Front Nutr. 2022 Oct 3;9:965376. doi: 10.3389/fnut.2022.965376. PMID: 36263304; PMCID: PMC9573946.
- Amrein K, Scherkl M, Hoffmann M, Neuwersch-Sommeregger S, Köstenberger M, Tmava Berisha A, Martucci G, Pilz S, Malle O. Vitamin D deficiency 2.0: an update on the current status worldwide. Eur J Clin Nutr. 2020 Nov;74(11):1498-1513. doi: 10.1038/s41430-020-0558-y. Epub 2020 Jan 20. PMID: 31959942; PMCID: PMC7091696.
