Vitamin
Vitamin D3
Cholecalciferol
The 'sunshine vitamin' doubles as a hormone precursor involved in brain function. Low vitamin D status is consistently linked with low mood — especially in winter and indoor lifestyles.
Our pick, and why
Choosing a vitamin d3 on iHerb
All three are D3 — the more effective form — so all clear the first bar. Sports Research is our pick: 5,000 IU with K2 as MK-7 (the longer-acting form), in a softgel with an oil carrier, and vegan-sourced from lichen. Thorne's liquid drops are excellent for precise dose control at 1,000 IU per 2 drops with K2 (as MK-4, a shorter-acting form), and the liquid format suits those who have difficulty swallowing capsules. NOW's 400 IU softgel fails the criterion: 400 IU is below the 1,000 IU floor supported by supplementation research, with no K2 and no stated oil base.
How we judge these
D3 not D2, dose 1,000–5,000 IU, K2 included, oil/fat base.
| Product | Product | Form | IU / serving | K2 included | Oil/fat base | Meets it | Link |
|---|---|---|---|---|---|---|---|
| Our pick Sports Research Vitamin D3 + K2 (VEGADELIGHT®) | D3 cholecalciferol (lichen) | 5,000 IU | Yes — MK-7 100 mcg | Softgel (oil base) | ✓ | iHerb → | |
| Thorne Vitamin D/K2 Liquid | D3 cholecalciferol | 1,000 IU / 2 drops | Yes — K2 MK-4 200 mcg | Liquid (oil-based drops) | ✓ | iHerb → | |
| NOW Foods Vitamin D-3 400 IU | D3 cholecalciferol (lanolin) | 400 IU | No | Softgel (no stated oil) | — | iHerb → |
- Sports Research Vitamin D3 + K2 (VEGADELIGHT®)Our pick
- Form
- D3 cholecalciferol (lichen)
- IU / serving
- 5,000 IU
- K2 included
- Yes — MK-7 100 mcg
- Oil/fat base
- Softgel (oil base)
- Meets our criterion
- ✓
- Thorne Vitamin D/K2 Liquid
- Form
- D3 cholecalciferol
- IU / serving
- 1,000 IU / 2 drops
- K2 included
- Yes — K2 MK-4 200 mcg
- Oil/fat base
- Liquid (oil-based drops)
- Meets our criterion
- ✓
- NOW Foods Vitamin D-3 400 IU
- Form
- D3 cholecalciferol (lanolin)
- IU / serving
- 400 IU
- K2 included
- No
- Oil/fat base
- Softgel (no stated oil)
- Meets our criterion
- —
Specs verified against live listings at time of writing and can change — confirm on the product page. Links are affiliate links; details.
Vitamin D behaves more like a hormone than a vitamin, and the brain is full of receptors for it. Observational studies repeatedly find that people with low vitamin D levels report lower mood — though trials show the clearest benefit when supplementation corrects an actual deficiency, rather than topping up someone who is already replete.
If you live at a northern latitude, work indoors, have darker skin, or simply spend most of the day inside, you are statistically quite likely to run low — which makes this one of the most rational “first checks” in any wellness routine.
What to look for
- D3 (cholecalciferol) rather than D2 — it raises blood levels more reliably
- Softgels with oil, or take alongside a meal with fat for absorption
- Consider pairing with vitamin K2 if you’re supplementing long-term