Daily SPF 50 and Vitamin D: What a Year-Long Trial Found

A question keeps resurfacing in skincare forums: if sunscreen blocks the UVB that makes vitamin D, does wearing it every day leave you short? Until recently the best answer was a shrug, because the real-world evidence used moderate-strength sunscreens. A year-long randomized trial published in late 2025 finally tested high-SPF daily use. Here is what it found, what it did not find, and how to act on it without giving up sun protection.

Why the question was open for so long

Vitamin D is made in skin after UVB exposure, and sunscreen reduces how much UVB reaches skin cells. Lab experiments consistently show that effect, but the authors of the new trial note it was uncertain whether it carries over to everyday life. People apply less sunscreen than the amount used in testing, miss spots, and still pick up incidental sun on a walk or a commute.

Earlier field trials of daily sunscreen with an SPF around 16 found no effect on the main blood marker of vitamin D status, 25-hydroxyvitamin D, usually written 25(OH)D. Before this trial, no study had examined daily high-SPF use in people over a long period.

What the Sun-D trial did

The Sun-D Trial, run by QIMR Berghofer in Australia, randomized 639 adults aged 18 to 70 who did not already use sunscreen routinely or take vitamin D supplements. One group applied SPF 50+ sunscreen, supplied by the study, as part of the morning routine on days when the UV index was forecast to reach 3 or higher. The control group used sunscreen at their own discretion. The trial ran for about a year, with blood measured at baseline in winter and spring 2022 and again at the end of summer and winter 2023.

Two design points matter. It was open-label, meaning participants knew which group they were in, although the sample handling and analysis were done blind to group. And it was in Australia, where UV levels are high, so results may not map neatly onto a northern US winter.

The numbers

Average baseline 25(OH)D was similar in both groups, at 63.5 nmol/L in the sunscreen group and 62.1 nmol/L in the control group. After the year, the adjusted mean change from baseline was 1.6 nmol/L in the sunscreen group and 6.8 nmol/L in the control group, a between-group difference of 5.2 nmol/L lower with daily sunscreen (95% confidence interval 3.2 to 7.2 lower).

Looking at deficiency, defined as below 50 nmol/L, 45.7% of the sunscreen group (139 of 304) fell below that line at the end, against 36.9% of controls (115 of 312). That works out to a prevalence ratio of 1.33. The effect was seen across most subgroups, was larger in people who followed the sunscreen instructions more closely, and persisted in people who did not take supplements.

How to read a 5 nmol/L gap

It is easy to over-read this in either direction. A 5.2 nmol/L difference is modest next to a baseline of about 63 nmol/L. But because many people sit near the cutoff, a modest shift moved a meaningful number of people across it. Note also that the control group was not sun-bathing; they used sunscreen when they chose to, so the comparison is routine use against discretionary use, not sunscreen against no sunscreen at all.

The authors' conclusion was that routinely applying high-SPF sunscreen gives lower 25(OH)D than discretionary use, and that regular sunscreen users may need vitamin D supplementation. They also took pains to say the finding is not a reason to stop wearing sunscreen. The lead investigators describe sunscreen as a cornerstone of skin cancer prevention and advise people not to change their sunscreen habits.

What the researchers actually recommend

The advice from the research team and Cancer Council Australia is consistent:

• Keep applying broad-spectrum SPF 50+ sunscreen when the UV index is 3 or above.
• Do not rely on deliberate sun exposure to top up vitamin D. The team says there is no evidence that sun exposure is more effective than supplements for maintaining levels.
• Consider supplementation if you wear sunscreen consistently as part of a daily routine, and manage vitamin D with your doctor's advice.
• Use sunscreen as one of several protections: clothing, a wide-brimmed hat, shade and sunglasses.

Cancer Council Australia adds that for most people a few minutes of incidental sun on most days when the UV index is 3 or higher is usually enough to maintain adequate vitamin D. That is a statement about incidental exposure, not a prompt to tan.

Who might want to pay closer attention

The trial excluded people who already took supplements, so it says little about them. If you apply sunscreen every day, live at a higher latitude, spend most of the day indoors, or have darker skin that naturally filters more UVB, your starting vitamin D status could differ from the study average. These are reasons to ask a clinician about a blood test, not conclusions drawn from the trial itself, which reported subgroup consistency by UV zone and exposure.

A practical takeaway

1. Keep your daily sunscreen. The trial gave no reason to drop it, and the authors explicitly advise against that.
2. Do not tan to compensate. Overexposure to UV remains the biggest controllable risk factor for skin cancer, as Cancer Council Australia states.
3. If you are a consistent daily SPF user, bring it up at your next check-up and ask whether a 25(OH)D test or a supplement makes sense for you.
4. Apply sunscreen generously and reapply as directed, since the effect on vitamin D was larger in people who followed the application instructions, and the same habit is what delivers protection.

The short version: daily high-SPF sunscreen lowers vitamin D a little, which is a manageable detail to discuss with a doctor, not a reason to skip sun protection.