Personalized vitamin D recommendations based on latitude and skin type to help combat deficiency

In a recent study published in Nutrients, researchers calculated the approximate time of sun exposure to maintain vitamin D levels by latitude, month, and skin type, taking into account conditions clear and cloudy skies for an active person in modest clothing.

The study highlights the importance of an individualized approach to assessing nutritional needs. It highlights the relationship between dietary intake, sunlight exposure and geographic factors, which may help develop strategies to combat widespread vitamin D deficiencies among different populations.

Vitamin D is vital for musculoskeletal health and has many other health benefits, but deficiency is widespread, due in part to insufficient dietary sources and limited exposure to sunlight. Public health strategies often include food fortification or supplementation, but the challenge is balancing vitamin D synthesis with the risks of overexposure to sunlight.

Average UV values at noon under clear skies for March 2004–2020. Although UVR is primarily dependent on latitude, it is also affected by ozone levels (less in the Southern Hemisphere, especially at high latitudes) and altitude (most noticeably in western South America, where the Andes Mountains are located). Study: Global Assessment of UVB Exposure Time to Maintain Adequate Vitamin D Levels

The study aims to provide precise recommendations, taking into account factors such as latitude, skin type and season, to inform national policies regarding food fortification, supplementation and sunlight exposure. Thus, it covers the difficulty of maintaining optimal vitamin D levels while minimizing health risks.

The researchers used global ultraviolet (UV) radiation data from the Global Ozone Monitoring Experiment (GOME). This data was initially presented as a UV index (UVI) and later converted into UV radiation effective for the synthesis of vitamin D.

This data was obtained from instruments attached to European Space Agency (ESA) satellites and provided continuous coverage from 2002 to the present through the TEMIS portal. The study focuses on clear-sky UVI data and all sky conditions, including cloud data where possible, to determine UV levels.

To estimate changes in vitamin D levels, we used calculations from a previous study that relate UV exposure in terms of standard dose of vitamin D (SDD) to changes in circulating levels of 25-hydroxyvitamin D (25OHD).

Analysis revealed different exposure times required to maintain vitamin D levels under clear and cloudy skies.

Under clear skies, exposure times for people with white skin varied from 3 to 15 minutes per 10 degrees of latitude, with longer times at higher latitudes due to lower sun angles and Antarctic ozone depletion.

People with skin type V required longer exposure times at all latitudes compared to skin types I-IV, while people with skin type VI experienced even longer exposure times, especially at higher latitudes.

With cloudy skies, the impact of cloudiness varied with latitude and season, increasing exposure time by about 15% in equatorial regions and up to an additional 60% at high latitudes.

Despite this, maintaining vitamin D levels remained achievable for people with white skin even at high latitudes outside the vitamin D winter period. However, for people with type VI skin, exposure times exceeded 15 minutes in equatorial regions and more than an hour in high latitudes. Latitudes under all sky conditions.

The study results highlight the importance of balancing oral intake and cutaneous synthesis of vitamin D, especially through exposure to sunlight, to effectively address deficiency. They also provide valuable insight into the ability to maintain vitamin D levels through sunlight exposure, taking into account variations in latitude and skin type.

Maintaining vitamin D status becomes difficult during winter due to reduced availability of sunlight, especially at higher latitudes. This highlights the need for alternative strategies, such as increasing sun exposure in summer or dietary supplementation. Changes in lifestyle and working conditions may affect vitamin D synthesis, especially for people with deeply pigmented skin at higher latitudes.

Strengths of the study include its comprehensive approach, providing recommendations for sun exposure timing for different skin types and latitudes. However, limitations are recognized, such as assumptions regarding the area of skin exposed and lack of consideration of cultural practices.

Future studies could examine additional factors influencing vitamin D synthesis, such as age and ethnicity, and refine exposure timing recommendations based on a better understanding of individual needs and behaviors. Overall, the study results provide valuable insights to guide public health strategies to combat vitamin D deficiency worldwide.