Jack Dorsey Launches Sun Day App to Track UV Exposure and Vitamin D Synthesis

Block CEO and Twitter co-founder Jack Dorsey has unveiled a new health-focused application called Sun Day that helps users monitor their sun exposure and vitamin D synthesis. The app represents Dorsey's latest venture into mobile application development, following his recent launch of the decentralized messaging service Bitchat.

How Sun Day App Works

Sun Day calculates vitamin D synthesis from UV exposure using a comprehensive multifactor model based on scientific research. The application is currently available through Apple's TestFlight platform, allowing users to test the beta version before its official release.

The app leverages location services to track the current UV index and estimate sun exposure based on the user's geographical position. To provide personalized recommendations, Sun Day requests user input including age, clothing type, and individual skin tone characteristics.

Integration with Apple Health Data

Sun Day integrates seamlessly with Apple's Health app ecosystem, incorporating historical data and HealthKit vitamin D records to enhance accuracy. The app aims to provide personalized and accurate estimates while maintaining conservative safety parameters to protect users from overexposure.

Manual Input Required for Operation

Unlike automated tracking systems, Sun Day requires manual user interaction to function properly. Users must tap a button when they begin sun exposure and tap again when returning indoors. This manual on/off toggle system ensures precise tracking of actual outdoor time spent in direct sunlight.

Dorsey explained that the app doesn't automatically detect light conditions but relies on user input to log each sun exposure session accurately.

Future Development Plans

The development team has outlined several improvements for future versions of Sun Day. Planned updates include more precise calculations based on user height and weight, seasonal adjustments for varying UV levels, and integration with actual vitamin D blood test results for enhanced personalization.

Part of Dorsey's App Development Learning Process

Sun Day marks Dorsey's second app launch within two weeks, following the beta release of Bitchat, a decentralized peer-to-peer messaging service that operates entirely over Bluetooth networks. When asked about the rapid app launches, Dorsey clarified that he was simply learning rather than executing a market flooding strategy.

The Block CEO revealed that he utilized Block's artificial intelligence assistant, Goose, to assist in creating these applications, demonstrating his exploration of AI-powered development tools.

Health Technology Innovation

Sun Day represents an innovative approach to personal health monitoring, addressing the growing awareness of vitamin D deficiency and the importance of balanced sun exposure. By combining location data, personal characteristics, and health metrics, the app provides users with scientifically-backed guidance for optimizing their vitamin D synthesis.

The application's conservative safety approach ensures users receive accurate exposure recommendations while minimizing risks associated with excessive UV exposure. This health-focused technology could potentially help users maintain optimal vitamin D levels through informed sun exposure practices.

Availability and Testing

Currently available exclusively through Apple's TestFlight platform, Sun Day allows early adopters to test the beta version and provide feedback before the official launch. The TestFlight availability indicates Dorsey's commitment to user feedback and iterative improvement before wider distribution.

The app's development demonstrates Dorsey's continued interest in creating practical technology solutions that address real-world health and wellness needs, expanding beyond his traditional focus on social media and financial technology platforms.