by Cezary | Awake Strong | March 2026
Two very different people end up in the same place.
The first one moved to Vietnam to build something. Business, career, a project.
Working 60-hour weeks, running on adrenaline and strong Vietnamese coffee. They're grinding - and somewhere along the way, their brains capacity stopped keeping up.
The second one moved here for the life. And honestly? It's good. Great food, warm weather, a nice apartment, finally some breathing room after years of hustle back home. They're not stressed. They're not overworked. Life is actually pretty good.
And yet.
They're reading the same paragraph twice. Forgetting names. Making small decisions that used to feel automatic now take effort. By 2pm the brain is just... offline.
The grinder expat thinks: "obviously, I'm burned out."
The lifestyle immigrant thinks: "I have no reason to feel this way."
That second thought is the more dangerous one. Because it keeps people from looking for answers.
"Is This Normal?" (Sort of. But Not Really.)
Brain fog is extremely common among expats in Vietnam - regardless of whether you're working 60-hour weeks or finally taking it easy.
The lifestyle immigrant often has it worse in a way. They've removed all the obvious stressors. They're sleeping more, eating tasty food, not in back-to-back meetings. And they still feel mentally slower than they were five years ago in a much harder life.
Which means the cause isn't stress. It may be something physiological. And it's been quietly building up.
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Brain fog isn't a diagnosis. It's a symptom. And it can come from a dozen different places.
Here are the most common causes I see in expats living in Vietnam:
1. Low Vitamin D (Almost Universal Here)
This one surprises people. "But there's sun everywhere!"
True. But you're spending time indoors, in AC, commuting in Grab cars, and when you ARE outside you're covered up or wearing SPF 50 because the UV is brutal. The lifestyle immigrant who brunch, cafe-hops, and works from co-working spaces is getting almost no meaningful sun exposure.
Vitamin D plays a direct role in neurotransmitter synthesis and brain function. When it drops below 30 ng/mL (optimal is 50-70), cognitive fog, low mood, and fatigue follow - even if the rest of your life looks fine on paper (or Instagram)
I'd estimate 70-80% of the expats I work with come in under 35. Many under 20.
2. Iron and Ferritin - Especially If You've Had Gut Issues
Vietnam food is incredible. It's also a challenge for your gut.
If you've eaten street food regularly, had repeated rounds of food poisoning, or spent time in rural areas - your gut lining has taken hits. That affects iron absorption over time.
Low ferritin (stored iron) is one of the most underdiagnosed causes of brain fog. Basic blood panels often only test hemoglobin - which looks "normal" even when ferritin is depleted.
Without adequate ferritin, your brain doesn't get enough oxygen-carrying capacity. You think slower. You get tired faster. You feel vaguely... dull.
3. Thyroid Function
The thyroid regulates everything - metabolism, body temperature, energy, mental clarity.
Sub-optimal thyroid function is common, and it doesn't always show up as "hypothyroid" on a standard panel. Most panels only test TSH. A full picture requires Free T3, Free T4, and often Reverse T3.
This one hits lifestyle expats particularly hard because the symptoms are easy to explain away: "I'm just traveling (or partying) too much", "I'm getting older", "maybe I need to be more active." Meanwhile, the thyroid has been running below par for a year.
4. Chronic Low-Grade Inflammation
Pollution in HCMC is among the worst in Southeast Asia. A few years of breathing it - regardless of how good your lifestyle is - means your body has been running a low-grade inflammatory response. Add to it the noise, the heat and some lifestyle factors and your oxidative stress may be higher than you'd think
Inflammation affects the blood-brain barrier. It's directly linked to cognitive fatigue, brain fog, and mood instability.
CRP and homocysteine levels tell this story clearly. They're cheap tests. Rarely included in standard expat health checks.
5. Sleep Architecture
You might be sleeping 8 hours and still wake up unrefreshed.
Heat, humidity, and noise in Saigon affect sleep quality, not just duration. Less time in deep sleep, more micro-awakenings. The brain never fully consolidates.
For the lifestyle immigrant: irregular schedule, late nights, alcohol with dinner, no fixed wake time - these disrupt your cortisol rhythm even when you're "relaxed." Your sleep hours increase but your sleep quality declines.
"But My Tests Were Normal"
This is the most frustrating thing I hear.
"I went to FV Hospital. Spent $350. They said everything is fine."
Here's the problem: standard blood panels check for *disease*, not *optimal function*.
A Vitamin D of 22 ng/mL is technically "not deficient" by some lab ranges. But it's nowhere near optimal for brain function.
Same with ferritin at 18. Or Free T3 in the lower third of range.
"Normal" means you don't have a diagnosable condition. It doesn't mean your brain has what it needs to run well.
This is especially frustrating for the lifestyle expat. You're not sick. But you're also not the sharp, clear-headed person you used to be - and you can't explain why.
What To Actually Test
If you're experiencing brain fog, these are the markers worth looking at:
Baseline essentials:
- Vitamin D (25-OH)
- Full iron panel: serum iron, ferritin, TIBC
- Thyroid: TSH, Free T3, Free T4
- CBC (complete blood count)
- Metabolic panel: glucose, HbA1c, liver/kidney markers
If the basics look "fine" but you still feel off:
- Homocysteine
- CRP (inflammation)
- Cortisol (ideally morning)
- B12 and folate
- Magnesium (RBC, not serum)
Where to test in HCMC: diag.vn is probably the easiest to run comprehensive panels. Budget $80-150 USD for a decent panel.
Bring your results to someone who reads them functionally - not just checking if you're in range, but where in the range you sit and what the pattern means.
The Pattern I Keep Seeing
I'm a Functional Health Coach working with expats in HCMC. Over the past year, I've noticed a consistent combination:
- Vitamin D under 35
- Ferritin under 30
- CRP normal or elevated (even slightly)
- Sleep that looks "ok on paper" but isn't restorative
It shows up in the burned-out entrepreneur and in the person living their best life. Vietnam is a beautiful place to live.
It's also genuinely hard on the body in ways that aren't obvious until you test.
Fix those things in the right order, and cognitive clarity comes back faster than people expect. Not because of some protocol. Just because you found the actual cause.
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If You Want to Know Where You Stand
I put together a free guide with the specific markers I recommend for expats in Vietnam - optimal ranges (not just lab reference ranges), and where to get tested in HCMC.
[Download the Recommended Markers guide →]
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*Questions or want to talk through your results? WhatsApp me - I respond same day.*
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*Cezary is a Functional Health Coach based in Ho Chi Minh City, working with expats who feel off but can't get straight answers from conventional medicine.*