Twitter co-founder Jack Dorsey has introduced a new application that merges health tech with sun exposure tracking as public interest in preventive health and digital wellness tools continues to grow. The app, called Sun Day, uses real-time UV data to estimate your Vitamin D synthesis, offering a personalised approach to sunlight exposure. Currently available in beta through TestFlight for iOS, the app reflects a broader trend toward using AI-powered health tools to improve lifestyle habits, boost immunity, and promote holistic well-being through smarter choices.
Jack Dorsey launches Sun Day app to track Vitamin D levels in your body; here’s how
Sun Day uses location-based services to calculate your local UV index and sunlight duration. Once the user inputs their skin type, clothing coverage, and logs their sun exposure manually, the app estimates:
- How much Vitamin D your body may have produced
- How long you can safely stay in the sun without risking sunburn
This tailored approach is especially relevant for individuals who may have Vitamin D deficiencies, such as those with limited outdoor time, darker skin tones, or higher latitudes with weaker sunlight. The app is part of Dorsey’s experimentation with open-source and AI-based coding tools. The Sun Day project is publicly available on GitHub, allowing developers to contribute or build on the code. It was developed alongside Goose, an AI-assisted development tool also built by Dorsey’s team. Both projects reflect his evolving role as a solo open-source developer exploring AI in health and communication.
Why Vitamin D is crucial for your health
Vitamin D is more than just a nutrient—it acts like a hormone in the body and supports multiple essential functions. Its role in maintaining overall health is well-established, especially in the areas of immunity, bone strength, and emotional well-being.Strengthens the immune systemVitamin D helps regulate immune responses, allowing the body to better fight off infections. A deficiency can impair immune function, making individuals more susceptible to illnesses such as the common cold, flu, and respiratory infections.Maintains bone health and prevents osteoporosisVitamin D enhances calcium absorption in the body, which is essential for building and maintaining strong bones. Without sufficient Vitamin D, bones can become weak and brittle, increasing the risk of fractures and conditions like osteoporosis and rickets.Supports mental and emotional well-beingLow Vitamin D levels have been linked to mood disturbances such as depression and fatigue. In particular, it plays a role in regulating mood by influencing brain chemicals. This is especially important in regions with limited sunlight, where people are at higher risk for seasonal affective disorder.A preventive approach to modern lifestyle challengesFor individuals living in areas with inconsistent sunlight or those who spend extended hours indoors, the app can serve as a preventive health tool. It empowers users to monitor and optimize their Vitamin D levels, helping reduce the risk of immune deficiencies, bone disorders, and mood-related issues commonly associated with modern indoor lifestyles.
How the Sun Day app might help
Source: Apple App Store
Developed by Jack Dorsey, the Sun Day app provides personalised, real-time estimates of Vitamin D production. It uses location-based UV data along with user inputs like skin type, clothing coverage, and duration of sun exposure. Based on this information, it calculates how much Vitamin D the user may have synthesized and offers guidance on how long they can stay in the sun safely.This could mark an important development in the health sector, as the app encourages users to track their vitamin D levels, a nutrient essential for the body. It may also help prevent harmful effects of UV exposure, such as sunburn, skin damage, and serious conditions like skin cancer.Also Read | Hot dogs, sodas, and fast food could be stealing 36 minutes from your life, new study finds
