Question 1

How much vitamin D can I produce in the sun compared to a pill?

Accepted Answer

A full-body exposure to 1 MED produces around 10,000–25,000 IU of vitamin D. A standard supplement capsule contains 400–2,000 IU. A 15–20 minute midday session in summer with arms and legs exposed can easily exceed a week of typical supplementation.

Question 2

Can I overdose on vitamin D from the sun?

Accepted Answer

No. Solar synthesis is self-limiting. Once pre-vitamin D3 accumulates in the skin, continued UVB converts it into inert compounds — lumisterol and tachysterol. Your body never produces toxic levels from sun exposure.

Question 3

What blood levels of 25-OH-D are considered optimal?

Accepted Answer

Below 20 ng/mL is deficient; 20–30 ng/mL is insufficient; 30–50 ng/mL is sufficient. The Endocrine Society considers 40–60 ng/mL optimal for non-skeletal benefits. Above 100 ng/mL carries toxicity risk from supplementation.

Question 4

Why is K2 recommended alongside D3?

Accepted Answer

Vitamin D3 increases calcium absorption. Vitamin K2 (MK-7) activates osteocalcin (directs calcium into bones) and matrix Gla protein (prevents arterial calcification). If you supplement more than 1,000 IU/day of D3, 100–200 mcg of MK-7 is recommended.

Question 5

When can I synthesize vitamin D from the sun?

Accepted Answer

Vitamin D synthesis requires a UV index of 3 or higher, which typically occurs when the sun is above 45–50° elevation. This depends on your latitude, time of year, and time of day. At latitudes above 35°N, synthesis is impossible during winter months.