Jack Dorsey, co-founder and former CEO of Twitter, has officially launched Sun Day, a wellness-focused app designed to help users monitor sun exposure and vitamin D intake for better health outcomes.
The launch of Sun Day comes shortly after Dorsey introduced Bitchat, an experimental messaging app that functions without an internet connection.
Sun Day combines location-based technology with user input to calculate UV exposure and provide personalized recommendations. By analyzing factors such as geographic location, skin type, clothing, and weather conditions, the app offers insights into the body’s vitamin D production.
“Sun Day allows you to manually track your time in the sun and gives estimates of your daily vitamin D intake,” the app’s description reads.
Among its core features are:
- Real-time UV Index monitoring based on your phone’s GPS.
- Vitamin D intake estimates adjusted for skin tone and clothing.
- Personalized burn limits, helping users avoid overexposure.
- Daily sunrise and sunset times.
- Cloud cover analysis to determine ideal sun exposure windows.
The app aligns with Jack Dorsey’s longstanding interest in biohacking, wellness, and personal optimization. Health experts have long emphasized the importance of vitamin D for immune health, bone strength, and mood regulation—especially as sedentary lifestyles and indoor work reduce sun exposure for many people.
While Sun Day is currently in its early rollout phase, it has already sparked interest among tech enthusiasts, health-conscious users, and biohackers, adding to Jack Dorsey’s growing portfolio of minimalist and decentralized digital tools.
Sun Day is expected to be available on both iOS and Android in the coming weeks.
