Vitamin D
Table of contents
Living in sunny Singapore, I didn’t expect to be low in vitamin D, but in April I was. Six months of a daily vitamin D3 supplement took me from “insufficient” to the upper part of “desirable”. This article covers what vitamin D does, why April’s number was worth fixing, and why I’ve now cut the dose back.
Snapshot
| April 2026 | October 2026 | Target | Status | |
|---|---|---|---|---|
| Vitamin D (25-OH) | 68.2 nmol/L | 181.2 nmol/L | >75 | ✅ on target |
Here’s the October result from my report, with the lab’s interpretive bands:
What it is
Vitamin D is more like a hormone than a typical vitamin. The skin makes it from sunlight, and a little comes from food. Its best-known job is helping the gut absorb calcium for strong bones, but it’s also involved in muscle function and the immune system.
The blood test measures 25-hydroxy vitamin D (25-OH D), the form the body stores. It reflects roughly the last couple of months of sun exposure and supplements.
My lab reports it in nmol/L, using these bands:
| Band | nmol/L |
|---|---|
| Deficient | <25 |
| Insufficient | 25–74.9 |
| Desirable | 75–249.9 |
| Possible toxicity | ≥250 |
What I’m aiming for
My doctor set a target of above 75 nmol/L, the bottom of the desirable band. Being comfortably in the band, rather than just over the line, makes sense for me. I train hard, I’m losing and regaining weight around competitions, and I want to look after my bones, muscles and immune system.
The other end matters too. I don’t want to drift towards 250, where too much vitamin D can start pushing calcium too high.
Why April was a problem
At 68.2 nmol/L I was in the “insufficient” band, below my 75 target. Not dramatically low, but low enough to fix.
It sounds odd in Singapore, but it’s common: most of my day is indoors, and when I am outside it’s often early morning or evening, or in clothes that cover most of my skin. Sunshine only helps if it actually reaches your skin.
The risks of staying low over the long run:
- Bones: less calcium absorbed, which over years means weaker bones. Not ideal in a sport where I get thrown and land on things.
- Muscle: low vitamin D is linked to poorer muscle function and recovery.
- Immunity: low levels are associated with picking up more infections, and a cold during a training camp costs weeks.
Why October is better
At 181.2 nmol/L, I’m well inside the desirable range. Of all my results, this one has the clearest explanation:
- Vitamin D3 supplement: from April I took 5,000 IU of vitamin D3 every evening. That’s a fairly high daily dose, so a jump of over 100 nmol/L in six months is about what you’d expect.
More time outdoors may have helped a little, but the supplement is almost certainly the main reason.
What’s next
- I’ve cut the dose to 3× a week. At 181 I’m comfortably in range, but daily 5,000 IU would keep pushing the number up, and I don’t want to creep towards the 250 “possible toxicity” line. About 2,000 IU a day on average should hold me somewhere sensible.
- Retest at my next blood test. That shows whether the lower dose keeps me above 75 without overshooting. If it lands somewhere in the 100s, I’ll keep this routine.
- If you’re thinking of supplementing yourself, get tested first. The right dose depends on where you start.
This is my own personal data, shared for interest only. It’s not medical advice.
Until next time, peace and love!