Vitamin D 101: Sunshine, Food & Supplements Explained

**Your immune cells carry vitamin D receptors—drop below 50 nmol L‑¹ and infection risk rises 40 %.**

- Target blood level: 75‑125 nmol L‑¹ (30‑50 ng mL‑¹) - 10‑15 min summer sun = 1000 IU - Food is limited: salmon, egg yolk, fortified milk - RDA: 600‑800 IU; UL: 4000 IU (adults)

A fat‑soluble pro‑hormone produced in skin (UV‑B) or obtained from diet; converted to active calcitriol, regulating **calcium uptake, immunity and gene expression**.

1. **Bone strength** – 20 % lower fracture risk when serum ≥ 75 nmol L‑¹. 2. **Immune modulation** – meta‑analysis (BMJ 2017) showed 12 % fewer acute respiratory infections with daily D. 3. **Mood & cognition** – deficiency linked to seasonal affective disorder.

- Frequent colds / flu - Bone pain, muscle weakness - Rickets in children; osteomalacia in adults

| Source | IU per serving | |--------|----------------| | Wild salmon (100 g) | 600‑1000 | | Egg yolk (1) | 40 | | Fortified cow’s milk (250 ml) | 120 | | Sun (face + arms, midday, 15 min, fair skin) | ~1000 |

- **Infants 0‑12 m:** 400 IU - **Adults 19‑70 y:** 600 IU (800 IU ≥ 70 y) - Test 25(OH)D every 6‑12 months if supplementing > 2000 IU day‑¹.

| Myth | Fact | |------|------| | “More sun is always better.” | After 20 min, skin degrades excess previtamin D to lumisterol. | | “You can get enough from food alone.” | Average diet supplies < 200 IU day‑¹. | | “Vitamin D is only for bones.” | It regulates > 200 genes, incl. immune pathways. |

👉 **Download our vitamin D tracker sheet** to log sun time & IU intake.

Short, sensible sun plus D‑rich foods and, when needed, a tested supplement keep your levels in the sweet spot for bones, immunity and mood.

1. Holick MF. *N Engl J Med* 2007. 2. Martineau AR et al. *BMJ* 2017. 3. EFSA DRV for vitamin D, 2024.