People who routinely apply a high SPF sunscreen over the course of one year are more likely to be vitamin D deficient than those who use sunscreen less frequently, an Australian study has found.
The QIMR Berghofer-led researchers said while regular sunscreen use was still recommended, their findings suggested it should be considered a risk factor for vitamin D deficiency by individuals and clinicians, alongside other risk factors.
The Australian open-label randomised controlled Sun-D Trial, published in the British Journal of Dermatology [link here], was the first trial to determine the effect of daily application of a SPF50+ sunscreen on vitamin D deficiency.
Other randomised controlled trials found negligible differences with low SPF sunscreens but these were conducted in areas with high ambient UV radiation.
“Sunscreen remains a cornerstone of skin cancer prevention, backed by decades of robust evidence,” said lead investigator Professor Rachel Neale from QIMR Berghofer’s Population Health Program, in Brisbane.
“Our findings simply suggest that people who are diligent about daily sunscreen use may want to consider vitamin D supplementation as a safe, effective and cheap way to maintain healthy vitamin D levels.”
The study involved 639 Australians (median age 52, 66% female) aged 18-70 with self-declared Fitzpatrick skin type 1 to 4 who were not regular sunscreen users.
Participants resided in the four eastern states of Australia and the ACT.
Half of the group were instructed to apply SPF50+ sunscreen on all days the UV index was forecast to reach ≥3 for a year, while the other half served as controls and used sunscreen according to their discretion over the same time period.
Vitamin D deficiency was defined as serum 25-hydroxyvitamin D [25(OH)D] concentration <50 nmol/L.
Findings showed the serum 25(OH)D concentration increased in both groups from baseline (winter/spring) to the end of summer, although the increase was significantly lower in the intervention group (11.7 versus 16.9 nmol/L, respectively).
The decrease from summer to winter was similar (about 20 nmol/L).
After 12 months, 46% of the sunscreen group were vitamin D deficient, compared to 37% in the control group, with an adjusted prevalence ratio (PR) of 1.33.
Findings from the per-protocol analysis were stronger than the intention-to-treat analysis, with the prevalence of vitamin D deficiency 49% and 35% in the intervention and control groups, respectively (adjusted PR 1.49).
The researchers said the effect on vitamin D deficiency was apparent across most subgroups, except for those who had high vitamin D status at baseline.
As for adverse events, skin rashes and acne were reported by 23 participants in the intervention group (7%) with six cases resulting in cessation of sunscreen.
Sunburn was reported by 71% and 43% of the control and intervention groups, respectively.
“In the Sun-D Trial, regular sunscreen application had a statistically significant, albeit modest, effect on serum 25(OH)D concentration. However, we observed a marked difference in the prevalence of vitamin D deficiency after approximately one year of use, and it is important to consider the potential impact over a longer period of use,” they said.
“Serum 25(OH)D concentration varies seasonally, being higher in summer and lower in winter. We observed this pattern in both groups. However, the increase from baseline (winter/spring) to the end of summer was smaller in the intervention group, and this appeared to be the driver of the higher prevalence of vitamin D deficiency at the end of the subsequent winter.
“We speculate that multiple annual cycles, with a lower serum 25(OH)D nadir in winter followed by a smaller increase over summer, could increase the risk of vitamin D deficiency, possibly severe, in regular sunscreen users.”