Researchers studied nearly 339,000 people to understand how genes and sun exposure work together to control vitamin D levels in our bodies. Using satellite data to measure how much UV light each person was exposed to based on where they lived, scientists discovered 162 new genetic variations that affect vitamin D. Interestingly, they found that people who get more sun exposure show stronger genetic effects on vitamin D levels. The study also suggests that vitamin D might be connected to our body’s internal clock, which controls sleep and metabolism. This discovery could help explain why vitamin D affects so many aspects of our health.

The Quick Take

  • What they studied: How genes and sun exposure together determine how much vitamin D your body makes and stores
  • Who participated: 338,977 people of White British ancestry from the UK Biobank study, with their sun exposure measured using satellite weather data based on where they lived
  • Key finding: Scientists found 162 new genetic variations linked to vitamin D levels that weren’t known before. The effect of these genes was stronger in people who got more sun exposure—those in the sunniest areas showed twice as much genetic influence (15.56%) compared to those in the least sunny areas (8.48%)
  • What it means for you: Your vitamin D levels depend on both your genes and how much sun you get. This research suggests that if you live in a sunny area, your genes may play a bigger role in your vitamin D levels. However, this is basic science research—it doesn’t yet change how doctors recommend vitamin D intake or sun exposure

The Research Details

This was a large genetic study using data from the UK Biobank, a collection of health information from hundreds of thousands of British people. Researchers used a clever method to measure sun exposure: instead of asking people how much time they spent in the sun (which people often get wrong), they used satellite weather data to calculate how much UV light hit each person’s home address on the day their blood sample was taken. They then looked at the entire genetic code of each participant to find which genetic variations were connected to vitamin D levels. The researchers used three different statistical approaches to find both direct genetic effects and cases where genes and sun exposure worked together to influence vitamin D.

Previous studies found some genes linked to vitamin D, but they didn’t account for sun exposure in a precise way. By using satellite data instead of guessing, this study could see how genes and environment interact more clearly. This interaction is important because it shows that your genes don’t work in isolation—they work differently depending on your environment. Understanding these interactions helps scientists figure out why vitamin D affects so many health conditions and why people in different climates might need different amounts of vitamin D.

This study has several strengths: it’s very large (nearly 340,000 people), it used objective satellite data for sun exposure instead of relying on people’s memory, and it was published in Nature Communications, a highly respected scientific journal. The researchers carefully adjusted their analysis for factors that could confuse results, like age, sex, and vitamin D supplements. One limitation is that the study only included people of White British ancestry, so the findings may not apply equally to people of other ethnic backgrounds, who may have different genetic variations affecting vitamin D

What the Results Show

The researchers identified 307 genetic variations connected to vitamin D levels, with 162 of these being completely new discoveries. This is significant because it nearly doubles the number of known genetic factors affecting vitamin D. The most striking finding was that the strength of genetic influence on vitamin D changed dramatically based on sun exposure. In people living in areas with the least sun (bottom 20%), genes explained about 8.5% of the differences in vitamin D levels between people. But in people living in the sunniest areas (top 20%), genes explained about 15.6% of the differences. This means that in sunny climates, your genes matter more for determining your vitamin D level, while in cloudy climates, sun exposure becomes the limiting factor regardless of your genes.

The study also discovered that many of the genes involved in vitamin D are connected to our body’s circadian rhythm—the internal clock that controls when we sleep, eat, and do other activities. One important gene they found is called BMAL1, which is a master controller of our circadian rhythm. This suggests that vitamin D and our body clock might be more connected than previously thought. The researchers also found genes linked to how our body processes fats (lipid metabolism), which could explain why vitamin D is known to affect cholesterol and other blood fats. These findings suggest that vitamin D might help coordinate seasonal changes in our metabolism.

Before this study, scientists had identified about 145 genetic variations affecting vitamin D through similar research. This new study more than doubled that number by using more precise sun exposure measurements and larger sample sizes. Previous studies often relied on people reporting their sun exposure, which is unreliable. By using satellite data, this research was able to detect genetic effects that were hidden in earlier studies. The discovery of the connection between vitamin D genes and circadian rhythm genes is relatively new and opens up a different way of thinking about why vitamin D is important for health.

The study only included people of White British ancestry, so we don’t know if these same 162 genetic variations affect vitamin D levels in people of African, Asian, or other ancestries—genetic variations can differ between populations. The sun exposure measurement, while more precise than asking people, was based on residential address and didn’t account for people spending time indoors or traveling. The study is observational, meaning it shows associations between genes and vitamin D but doesn’t prove cause and effect. Finally, this research identifies genetic variations but doesn’t explain exactly how they work or what they do in the body

The Bottom Line

This research doesn’t change current vitamin D recommendations yet, as it’s foundational science rather than clinical guidance. However, it suggests that people in sunnier climates may have more genetic variation in vitamin D production, while people in cloudier climates should focus more on dietary sources and supplements since sun exposure is limited. Current recommendations to get 10-30 minutes of midday sun exposure several times per week (depending on skin tone and location) remain appropriate. If you have concerns about your vitamin D levels, ask your doctor about testing and personalized recommendations based on your location and genetics

This research is most relevant for people interested in understanding why vitamin D recommendations vary by location and why some people seem to maintain good vitamin D levels with less sun exposure than others. It’s particularly interesting for people living in northern climates with limited sun, people with darker skin tones (who produce less vitamin D from sun exposure), and those with vitamin D deficiency despite adequate sun exposure. Researchers studying vitamin D, circadian rhythms, and seasonal health changes should pay close attention. People taking vitamin D supplements or concerned about their vitamin D levels should discuss this research with their healthcare provider, though it doesn’t change current medical advice

This is basic research that explains how vitamin D works at the genetic level. It may take 5-10 years before these discoveries lead to changes in clinical practice or personalized vitamin D recommendations. In the near term, this research helps explain individual differences in vitamin D levels and may eventually lead to genetic testing to predict who needs more vitamin D supplementation

Want to Apply This Research?

  • Track your vitamin D levels (through blood tests) twice yearly—once in winter and once in summer—to see how your personal vitamin D varies with seasons. Record your location, sun exposure time, and any supplements taken. This personal data can help you understand whether you’re a ‘high responder’ or ’low responder’ to sun exposure
  • Use the app to log daily sun exposure time and location, then correlate it with vitamin D test results over several months. Set reminders for vitamin D supplementation during winter months or if you spend most time indoors. Track any changes in energy, mood, or sleep quality alongside vitamin D levels to see if you notice seasonal patterns
  • Create a seasonal vitamin D tracking plan: test levels in January and July each year, log average daily sun exposure by month, and note any supplements taken. Use the app to identify your personal ‘vitamin D pattern’ and adjust sun exposure or supplementation accordingly. Share this data with your healthcare provider to personalize recommendations based on your genetics and location

This research is foundational science that explains how genes and sun exposure influence vitamin D levels. It does not provide medical advice or change current clinical recommendations for vitamin D intake or sun exposure. Vitamin D levels should only be interpreted by qualified healthcare providers in the context of your individual health. If you have concerns about your vitamin D status, vitamin D deficiency, or how much sun exposure is appropriate for you, consult with your doctor or a registered dietitian. This is especially important for people with skin cancer risk, those taking medications that affect vitamin D, or those with conditions affecting vitamin D absorption. Do not change your sun exposure habits or vitamin D supplementation based solely on this research without medical guidance.