Jack Dorsey’s Sun Day App Lets You Track Every Second of Sun Exposure

Jack Dorsey, co-founder of Twitter and CEO of Block, has launched a new app called Sun Day that helps users track their sun exposure and estimate vitamin D synthesis. The app uses location data and personal inputs to provide tailored feedback.

Available in beta through Apple’s TestFlight, Sun Day requires users to manually log their time spent outdoors. It factors in variables like skin tone, clothing, and age to calculate vitamin D production.

How does Sun Day track your sun exposure?

Sun Day uses your device’s location to monitor the current UV index and combines this with your manual input for when you go outside and return indoors. This approach aims to provide a personalized estimate of your sun exposure.

The app also integrates data from Apple Health, including historical vitamin D records, to refine its calculations and provide a more accurate picture of your vitamin D levels.

Did you know?
Vitamin D synthesis in the skin is triggered by UVB rays from sunlight, and its levels can vary widely depending on skin tone, location, and time spent outdoors.

What features make Sun Day unique?

Unlike apps that rely solely on light sensors, Sun Day uses a manual toggle system to log sun exposure sessions. This method avoids inaccuracies from ambient light and focuses on user engagement.

The app’s white paper highlights its conservative approach to estimating vitamin D synthesis, prioritizing user safety while delivering personalized insights.

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Jack Dorsey’s approach to health tracking

This is Dorsey’s second app launch in two weeks, following Bitchat, a decentralized messaging service. He credits Block’s AI assistant, Goose, for helping develop these projects.

Dorsey emphasizes that these apps are part of his learning process, exploring new technologies and health tracking methods without rushing to flood the market.

Future improvements planned for Sun Day

The development roadmap includes adding more precise calculations based on height, weight, seasonal variations, and actual vitamin D blood test results.

These enhancements aim to make Sun Day a comprehensive tool for managing sun exposure and overall health, reflecting Dorsey’s commitment to innovation and user safety.