Vitamin D2026-05

Update on Vitamin D Status and Seasonal Variation in a Non-Supplemented Population Living in a High Polluted Urban Area-A Cross-Sectional Study.

Bertoldo Francesco, Bortolus Renata, Filippini Francesca, Chiaffarino Francesca et al. — Nutrients

Summary

This study looked at vitamin D levels in healthy adults living in a polluted city in Northern Italy who were not taking vitamin D supplements. Researchers found that most participants had sufficient vitamin D, and levels were generally better than previously thought for the region. However, being overweight or obese was linked to lower vitamin D levels, highlighting the importance of healthy weight management for vitamin D status.

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Key points

The study examined vitamin D levels in healthy, non-supplemented adults in a polluted urban area of Northern Italy.
Most participants had adequate vitamin D levels, which were higher than previously reported for the region.
Seasonal changes in vitamin D (higher in summer, lower in winter) were still observed.
Individuals who were overweight or obese were more likely to have insufficient vitamin D levels.

What the study looked at

This study aimed to understand the current vitamin D status and how it changes with the seasons in healthy adults living in a polluted city in Northern Italy, especially those not taking vitamin D supplements. Previous data for this region was limited, and researchers wanted to see if pollution or latitude affected vitamin D production from sunlight. Researchers conducted a retrospective cross-sectional study involving 534 healthy blood donors, aged 18 to 65, from Verona, Italy. They collected blood samples between April 2016 and May 2018 to measure vitamin D levels and gathered information on participants' lifestyles and health. The data was then analyzed to observe seasonal patterns and other influencing factors. The study found that most healthy, normal-weight individuals had sufficient vitamin D levels, with only a brief period of insufficiency (one to two months) each year. Surprisingly, these levels were higher than what had been reported in the same area in the past, though the typical seasonal variation (higher in summer, lower in winter) remained. A significant finding was that individuals who were overweight or obese were less likely to achieve adequate vitamin D levels through sun exposure alone.

Dietary takeaway

This study suggests that even in a polluted urban environment, healthy individuals who don't take supplements can maintain good vitamin D levels, especially if they are at a healthy weight. While sun exposure is crucial, dietary choices like consuming fatty fish (salmon, mackerel), fortified foods (milk, cereal), and some mushrooms can help support vitamin D intake. Remember, this is just one study, and individual needs for vitamin D can vary, so it's always best to consult a healthcare professional for personalized advice.

Abstract

Serum concentrations of 25-hydroxyvitamin D [25(OH)D] are associated with the risk of several chronic and acute diseases. However, updated data on vitamin D status in Mediterranean countries, including Italy, remain limited, hindering effective public health strategies. To assess serum 25(OH)D levels and their seasonal variation in healthy blood donors aged 18-65 years living in Northern Italy and not taking vitamin D supplements. Given the latitude and the high levels of environmental pollution, cutaneous vitamin D synthesis may be impaired in this population. Recent Italian guidelines on supplementation emphasize the need for updated data on the prevalence of hypovitaminosis D and seasonal variation in endogenous vitamin D synthesis. In this exploratory retrospective cross-sectional study, 534 blood donors (268 men and 266 women) attending the Transfusion Medicine Unit of the Verona University Hospital were enrolled between April 2016 and May 2018. Serum 25(OH)D concentrations were analyzed by season. Clinical, lifestyle, pharmacological and dietary characteristics were also collected. Among healthy, normal-weight individuals, the prevalence of vitamin D insufficiency (25(OH)D < 50 nmol/L) was low and limited to one-two months per year. Overweight and obesity significantly reduced the likelihood of achieving adequate 25(OH)D levels through cutaneous synthesis for several months. Mean 25(OH)D concentrations were higher than those previously reported in the same area, while seasonal variation remained preserved. In a relatively small non-supplemented population of blood donors living in a high polluted urban area of Northern Italy, seasonal vitamin D synthesis seems to be preserved. These updated data show higher 25(OH)D levels compared to past findings. Although these data certainly warrant further validation through a national survey involving other regions of Italy and in not selected population, they appear to be in line with the SIOMMMS recommendations against indiscriminate serum 25(OH)D testing and against routine supplementation for healthy normal-weight individuals under 70 years.

View on PubMed →DOI: 10.3390/nu18101614