Short answer: no — not on its own. In a randomised, placebo-controlled trial of trained cyclists, UVA light alone produced no significant improvement in 10-mile time-trial performance and no reduction in the oxygen cost of exercise — a point the authors state directly in their own conclusion.
A gain appeared in only one of the four conditions tested: UVA combined with dietary nitrate. But nitrate is a known performance aid, and light alone did nothing, so that combined result can’t be used to claim light makes you faster. It’s a weak, hypothesis-generating signal at best.
What the study does show cleanly is that UVA has a real effect on the vascular system — lowering blood pressure and influencing nitric-oxide availability. That’s why light still belongs in the periodisation conversation. But the gap between “affects your physiology” and “improves your performance” is exactly where careful reading matters, so here’s the full picture.
How does light reach your bloodstream?
The mechanism runs through nitric oxide (NO) — the molecule that relaxes blood vessels, lowers blood pressure and improves blood flow. Your skin isn’t a passive barrier here: it holds large stores of NO precursors. When UVA wavelengths (320–400nm — not the burning UVB band) strike the skin, they release NO from those stores by photodecomposition, independent of the usual enzymatic pathway.
Greater NO availability has been linked to a lower oxygen cost of exercise, which is the same logic behind beetroot juice and nitrate supplementation — those raise NO through a separate dietary route (nitrate reduced to nitrite by oral bacteria, then to NO). Two different doors into the same room. The study opened both and measured what happened.
What did the study test?
Nine trained male cyclists and triathletes (VO₂max ~53 ml/kg/min) each completed a 16.1km (10-mile) time trial under four conditions, in randomised, counterbalanced order:
- Control — placebo gel + sham light
- UVA only — placebo gel + UVA exposure
- Nitrate only — nitrate gel + sham light
- Nitrate + UVA — both together
Nitrate dose was ~8.1 mmol, taken 2.5 hours before riding. Light dose was 20 J/cm² of UVA — roughly 30 minutes of midday summer sun in southern Europe — to one side of the body over 22 minutes, face and eyes shielded.
It’s a clean crossover: every rider was their own control, the right design for detecting small effects.
What did it actually find?
Only one condition produced a statistically significant performance gain — and it wasn’t light.
- UVA alone: 1450s vs 1469s control — not significant (P=0.122).
- Nitrate alone: 1455s — not significant (P=0.106).
- Nitrate + UVA: 1447s — significant (P=0.005), about 22 seconds faster than control.
Critically, UVA alone also failed to reduce the oxygen cost of steady-state cycling (P=0.381). So on its own, light moved neither the clock nor the efficiency that usually drives it.
The honest interpretation of the one positive result: the study was underpowered to detect the single interventions (post-hoc statistical power was 0.47 for UVA alone and 0.51 for nitrate alone, versus 0.97 for the combination).
Nitrate is robustly ergogenic in the wider literature. The most parsimonious reading is that nitrate did the work, the small sample simply couldn’t show nitrate alone, and UVA’s marginal contribution to the combined result is unproven — not that light is an independent performance aid.
So is the “sunlight makes you faster” framing wrong?
For performance, on this evidence — yes, it’s an overread. What’s not an overread is the vascular effect. UVA exposure on its own lowered blood pressure from baseline and attenuated the natural decline in plasma nitrite that comes from resting before a trial.
The combined nitrate+UVA condition produced the largest nitrite rise of all (456 nM vs 215 nM in control) and was the only one to significantly lower mean arterial pressure.
So light genuinely reaches into the NO/vascular system. It just didn’t convert that into a measurable performance benefit when used alone in this protocol. Holding both of those facts at once — real mechanism, unproven performance claim — is the accurate position.
The honest verdict
- UVA light alone did not improve performance. The paper says so; the numbers say so. Anyone citing this study as proof that sunlight makes athletes faster has read the headline, not the result.
- The only significant gain was the nitrate+UVA combination — and it can’t be cleanly credited to light, because light alone did nothing and nitrate is the established actor.
- It’s nine men, one small study. Promising as a hypothesis about whether light might augment nitrate. Nowhere near settled.
- The skin-cancer trade-off is real, and the authors flag it. They advise against regular or larger UVA doses given the increased skin-cancer risk, particularly for pale-skinned individuals. For a Northern-European cycling population, that alone closes the door on UVA as a deliberate performance tactic.
A scientist’s read: good evidence for the mechanism, no basis for a protocol, and certainly no basis for chasing sun.
Then why does light still matter as a training variable?
Because the mechanism is real even when this particular performance result isn’t there. Light measurably modulates the nitric-oxide and vascular system that sets the ceiling on endurance — that’s worth understanding and managing, just not via deliberate UV dosing. The sensible, lower-risk versions of the same lever:
- The dietary route is the safe, evidenced one. If the target is raised NO and a lower oxygen cost of exercise, nitrate (beetroot, nitrate-rich vegetables) is well-supported and carries none of the UV risk.
- Sensible daylight, not UV dosing. Regular outdoor light supports vascular and circadian function through related pathways without seeking the erythemal doses this study used.
- Treat sun exposure as an uncontrolled variable.
- A sharp methodological point from the authors: season and latitude shift your baseline NO physiology. If you compare training or test data across the year, sun exposure is a confounder most athletes never account for. Managing light partly means measuring it.
If you're getting your daylight the sensible way — outdoors, without chasing UV — this is the sunscreen to do it in. Broad-spectrum SPF30 with maximum 80-minute water and sweat resistance, and a breathable formula that doesn't block pores or blunt the sweating you rely on to thermoregulate over a long ride.
Light belongs in the same model as heat, cold and altitude — a real input into performance physiology with a dose-response and a risk profile. This study is a good reminder that “real mechanism” and “proven ergogenic” are not the same claim.
Frequently asked questions
Does UVA light or sunlight make you a faster cyclist?
Not on its own, on this evidence. UVA alone produced no significant improvement in time-trial performance and no reduction in the oxygen cost of exercise. A gain appeared only when UVA was combined with dietary nitrate, and that can’t be attributed to the light.
So what did the light actually do?
It had a vascular effect — lowering blood pressure from baseline and influencing nitric-oxide availability — without translating into a standalone performance benefit.
Should I get sun exposure before a race?
No. The study doesn’t support it, and the researchers specifically advise against deliberate UVA exposure because of skin-cancer risk, especially for pale-skinned athletes. Dietary nitrate is the safe way to target the same NO mechanism.
Is this strong evidence?
It’s a well-designed but small (n=9) crossover trial, underpowered for the single interventions. Treat it as a hypothesis about light possibly augmenting nitrate — not as established fact.
Does this disprove that light is a training variable?
No. Light demonstrably affects the vascular/NO system. This study just shows that affecting physiology and improving performance are different claims — and only the first is supported here.
Source: Muggeridge DJ, Sculthorpe N, Grace FM, Willis G, Thornhill L, Weller RB, James PE, Easton C. “Acute whole body UVA irradiation combined with nitrate ingestion enhances time trial performance in trained cyclists.” Nitric Oxide 48 (2015) 3–9. doi:10.1016/j.niox.2014.09.158
Sun Endurance reads the primary literature and reports what it does and doesn’t show. We don’t claim performance where the evidence isn’t there.
