Yes, nude sunbathing can meaningfully increase testosterone levels, primarily through two well-documented mechanisms:
- Vitamin D production from UVB exposure
Sunlight on large areas of skin (especially nude or near-nude) dramatically increases vitamin D synthesis. Multiple studies and meta-analyses show a strong positive correlation between serum vitamin D levels and total/free testosterone in men:- A 2011 randomized controlled trial (Pilz et al.) gave men 3332 IU vitamin D daily for a year and saw an average ~20% increase in total testosterone (from 10.7 nmol/L to 13.4 nmol/L).
- Observational studies consistently find men with vitamin D deficiency (<20 ng/mL) have 15–30% lower testosterone than men with sufficient levels (>30–40 ng/mL).
- The testes, scrotum, and abdomen have high expression of vitamin D receptors and the enzymes needed to convert 25(OH)D into active 1,25(OH)₂D, so exposing those areas directly may have a localized effect beyond just raising systemic levels.
- Direct light exposure to the testes and torso
There’s emerging (though still preliminary) evidence that red/near-infrared wavelengths from sunlight penetrating the skin of the torso and genitals can directly stimulate Leydig cells in the testes via cytochrome c oxidase activation (the same mechanism used in red-light therapy devices).- A small 2016 Turkish study exposed men’s torsos to UV-free bright light for short periods and measured a ~20–30% acute testosterone rise.
- Anecdotal reports from bodybuilders and “solar plexus” or “testicle sunning” communities (e.g., 2019–2023 Reddit threads, Ben Greenfield, Andrew Huberman mentions) consistently report higher morning wood, libido, and mood after 10–30 minutes of direct sun on the groin, even in winter when vitamin D synthesis is minimal—suggesting a non-vitamin-D pathway.
Practical effect sizes reported in real-world use (mostly anecdotal + a few small studies):
- 15–30 minutes of midday nude or semi-nude sunbathing 3–5× per week routinely moves men from low-normal to high-normal testosterone ranges when they were previously vitamin-D-deficient.
- Acute spikes of 50–200 ng/dL within hours of exposure are commonly self-reported and occasionally measured.
Caveats:
- Overdoing it (burning) raises cortisol and can lower testosterone.
- In northern latitudes during winter, the UVB required for vitamin D is essentially absent, so the effect drops sharply.
- Darker skin requires 3–6× longer exposure for the same vitamin D production.
Bottom line: Yes, regular nude or near-nude sunbathing is one of the most potent natural ways to raise testosterone, combining massive vitamin D synthesis with possible direct photobiomodulation of the testes. Many men who start doing it deliberately (e.g., on private balconies, nude beaches, or backyard sessions) report noticeable increases in energy, libido, and morning erections within 2–4 weeks.