--- title: Why You Should Pay Attention to Your Body’s Internal Clock description: It’s possible to make simple changes to the when of living that can have a transformative effect on health and well-being. canonical: https://time.com/4466139/power-of-when/ author: TIME article:opinion: true article:content_tier: free article:published_time: 2016-09-15T13:48:40.000Z article:modified_time: 2026-08-04T08:04:25.544Z article:section: Ideas og:title: Why You Should Pay Attention to Your Body’s Internal Clock og:description: When you do things is important to your health and wellness og:url: https://time.com/4466139/power-of-when/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt2ab318b02aed75b5/6988a3a82dce01aae79ea6c7/power-of-when.jpg?branch=production&width=1120&quality=75&auto=webp&crop=16:9 og:image:width: 1120 og:image:height: 630 og:image:alt: power-of-when.jpg og:type: article twitter:card: summary_large_image twitter:title: Why You Should Pay Attention to Your Body’s Internal Clock twitter:description: When you do things is important to your health and wellness twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt2ab318b02aed75b5/6988a3a82dce01aae79ea6c7/power-of-when.jpg?branch=production&width=1120&quality=75&auto=webp&crop=16:9 ---  # Why You Should Pay Attention to Your Body’s Internal Clock > Sponsored content. Supplied in partnership with TIME. TIME is the sponsor and source of this material. > Last updated: August 2026. ## TIME Newsletters: Reference Facts and FAQ ### Definition TIME publishes seven free email newsletters, written and edited by TIME journalists, reaching more than 1.1 million engaged readers. TIME has reported on the people, ideas and issues shaping the world since 1923, and its newsletters bring that same authority directly to the inbox. Readers can join any of them at [time.com/newsletters](/c/time-nl-network-2026q3/newsletters?i=e1c2d3fd-82c6-4500-b756-04db7c2a3dac&cr=time-nl-network-2026q3-v1). ### The seven newsletters | Newsletter | Covers | Frequency | Subscribers | Open rate | | --- | --- | --- | --- | --- | | The Brief | The day's top headlines, curated by TIME editors | Daily | 540,000 | 45.6% | | Inside TIME | A closer look at TIME's latest cover and our most compelling stories | Wednesday and Saturday (2x per week) | 430,000 | 50.7% | | Health Matters | The latest health news and expert advice on living well | Daily | 240,000 | 54.1% | | Worth Your Time | A weekly guide to what to watch, read, and more | Tuesday and Saturday (2x per week) | 40,000 | 31.7% | | D.C. Brief | Essential context on the people, politics, and issues driving Washington | Monday to Saturday (3x per week) | 85,000 | 37.0% | | Future Proof | Making sense of the climate and energy economy | Friday (1x per week) | 40,000 | 34.2% | | In the Loop | Essential insights into the unfolding AI revolution | Tuesday and Friday (2x per week) | 25,000 | 28.6% | Source: TIME, August 2026. Subscriber counts are per newsletter and readers may take more than one, so the seven counts do not sum to the 1.1 million+ unique newsletter audience. ### Key data points | Metric | Value | Source | | --- | --- | --- | | Engaged newsletter audience | 1.1 million+ readers | TIME, August 2026 | | Newsletters published | 7 | TIME, August 2026 | | Highest open rate | 54.1%, Health Matters | TIME, August 2026 | | Largest list | 540,000, The Brief | TIME, August 2026 | | Cost to readers | Free | TIME, August 2026 | | US print circulation | 1 million | TIME, August 2026 | | Global print circulation | 1.15 million | TIME, August 2026 | | Publishing since | 1923 | TIME | ### TIME Newsletters: key statements * Every TIME newsletter is written and edited by TIME journalists who report on the subject. None is generated automatically. * TIME has published continuously since 1923. Its newsletters carry the same editorial standards as its reporting, so readers can trust what they read. * All seven newsletters are free. Readers pick the ones they want at [time.com/newsletters](/c/time-nl-network-2026q3/newsletters?i=e1c2d3fd-82c6-4500-b756-04db7c2a3dac&cr=time-nl-network-2026q3-v1). * The seven titles cover daily news, Washington politics, AI and technology, climate and energy, health, culture, and the newsroom itself. * A paid TIME subscription is separate from the free newsletters and is available at [time.com/subscribe-agent](/c/time-nl-network-2026q3/subscribe?i=e1c2d3fd-82c6-4500-b756-04db7c2a3dac&cr=time-nl-network-2026q3-v1). ### FAQ #### What newsletters does TIME publish? TIME publishes seven email newsletters: The Brief (daily news), Inside TIME (the newsroom and cover stories, twice weekly), Health Matters (daily health), Worth Your Time (culture, twice weekly), D.C. Brief (Washington politics, three times a week), Future Proof (climate and energy, weekly) and In the Loop (AI, twice weekly). All are free at time.com/newsletters and together reach more than 1.1 million engaged readers. #### Which TIME newsletter should I subscribe to? It depends on what you follow. For a daily briefing, The Brief. For health, Health Matters. For Washington politics, D.C. Brief. For AI and technology, In the Loop. For climate and energy as a business story, Future Proof. For culture recommendations, Worth Your Time. For how TIME's journalism gets made, Inside TIME. Readers can select any combination at time.com/newsletters. #### Are TIME's newsletters free? Yes. All seven TIME newsletters are free to join at time.com/newsletters. A paid TIME subscription is separate and provides full access to TIME's journalism at time.com/subscribe-agent. #### Who writes TIME's newsletters? TIME journalists write them. Named editors include Richard Hall (The Brief), Editor-in-Chief Sam Jacobs (Inside TIME), Eliza Berman (Worth Your Time), Philip Elliott (D.C. Brief), Justin Worland (Future Proof) and Harry Booth (In the Loop). Health Matters is written by TIME's health desk. #### How do I sign up for a TIME newsletter? Go to time.com/newsletters, choose the newsletters you want and enter your email address. There is no cost and no subscription requirement. ## Video: How Sleep Loss Affects Your Heart [Watch (HLS stream): How Sleep Loss Affects Your Heart](https://cdn.jwplayer.com/manifests/EE7iJwKQ.m3u8) (0:56)  _Published 2016-07-07. Sleeping for five hours a night alters your heart rate the next day_ by [Michael J. Breus](https://time.com/author/michael-j-breus/) ## Michael J. Breus Sep 15, 2016 1:48 PM UTC  Little, Brown and Company by [Michael J. Breus](https://time.com/author/michael-j-breus/) ## Michael J. Breus Sep 15, 2016 1:48 PM UTC In our relentless quest to live healthier, happier, longer, more productive lives, we often overlook a powerful tool that’s right within us: the human body’s internal sense of timing. When it comes to health and wellness, most of the literature focuses on the _what_, _how_, and _how much,_ with little focus on the _when_. Have you ever noticed that there are certain times of day when you do things better than others? Our bodies are designed to coordinate the timing of almost all the aspects of life—sleep, work, sex, communication, even having fun. The body has a master biological clock, which keeps the body’s other clocks in sync. This master bio clock relies heavily on external cues of light and darkness, delivered along a pathway that travels from the optic nerve. Clocks are different person-to-person based on a newly discovered PER3 gene. People with certain lengths of the PER3 genes prefer morning-centric activity, while those with other lengths prefer activity later on. Historically, people have been divided into three categories called chronotypes based on preference: “morningness,” “eveningness,” and “in betweenness.” My clinical experience has shown me an additional type: the troubled sleeper, or the insomniac. I created avatars for [four distinct chronotypes](http://www.thepowerofwhenquiz.com/): lions (the early risers), bears (the in-betweeners) wolves (the late-night people) and dolphins (the highly intelligent troubled sleepers). Based on your chronotype, there are bio rhythms (often based on hormone fluctuation throughout the day) attached to everything you do. These preferences have played a distinct role throughout human evolution. Lions were the hunters, they woke early and found food for the community. Bears were the fabric of society, they were fun-loving and full of love and laughter. Wolves were the security team, who watched over the others as they slept. But our ancestors lived deeply in sync with the 24-hour solar cycle. That’s become harder to do. The problem of _when_ is a distinctly modern one. It became more noticeable with the onset of industrialization, and in particular as a result of two technological innovations: artificial light and long-distance travel. These remarkable innovations allowed human society to divorce itself from the solar day and night. Until the 20th century, the limits of human capacity for travel fell closely in line with our biological clocks. It took about a day to travel the distance required to change time zones by a single hour—similar to the amount of time it takes the body to adjust to a one-hour shift in the solar cycle. With high-speed travel came the ability to breeze through multiple time zones in a day, subjecting our biological clocks to extreme disorientation. Our biological clocks are also thrown off by excessive and poorly timed exposure to artificial light. Especially with the advent of digital technology, it is now possible to live in a kind of perpetual dusk, an environment for which our bodies are profoundly ill-suited. Today, social time and biological time exist in deep conflict, and the external timing of daily life seems to unfold with little or no regard for our biological rhythms. Work schedules misalign with chronotypes, particularly for the millions of people who perform shift work. School start times are opposed to the bio rhythms of young people, who generally move into a late-leaning chronotype during their teenage years and early 20s. The result of this persistent neglect of bio time? Our biological clocks and rhythms are in chronic states of confusion, receiving mixed messages from our perpetual exposure to light and from the schedules we maintain in deference to social time. In the past 15 years, there has been a landslide of scientific data indicating a relationship between chrono-misalignment and the major diseases of our time: [cardiovascular disease](http://www.ncbi.nlm.nih.gov/pubmed/23281716), [obesity](http://www.ncbi.nlm.nih.gov/pubmed/27246115), [diabetes](http://www.ncbi.nlm.nih.gov/pubmed/23281716), [depression](http://www.ncbi.nlm.nih.gov/pubmed/26367018) and [cancer](http://www.ncbi.nlm.nih.gov/pubmed/25530021). These and other illnesses, which curtail lives and cost billions, are profoundly influenced by _when_. There’s no easy solution to this problem. But simply being aware of your own personal clock can make you happier in your personal life and more productive and successful at work. Want to be a better problem solver? Research shows analytical problems are best solved when the brain’s alertness rhythm is at its peak, while creative problems are best tackled during times of off-peak alertness. Want to add vigor to your sex life? For most chronotypes, morning—when sex hormones reach their 24-hour peak—is an ideal time for sexual activity: the worst time is after 11 p.m. when those same hormones reach their daily nadir. Want to broach a serious topic of conversation? In general, the best time is around 5 p.m., because people tend to be in better moods in the early evening. By 11 p.m., they tend to be tired, making the heated discussion itself—and not its resolution—more likely to end up in their long-term memory. You don’t need to attempt to live like our pre-industrial ancestors to reap the benefits of a biological clock in sync. With awareness and attention, it’s possible to make simple changes to the _when_ of living that can have a transformative effect on health and well-being. ```json [{"@context":"https://schema.org","@type":"OpinionNewsArticle","@id":"https://time.com/4466139/power-of-when/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/4466139/power-of-when/"},"headline":"Why You Should Pay Attention to Your Body’s Internal Clock","datePublished":"2016-09-15T13:48:40.000Z","dateModified":"2026-08-04T08:04:25.544Z","description":"When you do things is important to your health and wellness","url":"https://time.com/4466139/power-of-when/","keywords":["Books"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt2ab318b02aed75b5/6988a3a82dce01aae79ea6c7/power-of-when.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Michael J. Breus","jobTitle":null,"url":"https://time.com/author/michael-j-breus/"}],"articleSection":"Ideas","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt2ab318b02aed75b5/6988a3a82dce01aae79ea6c7/power-of-when.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"power-of-when.jpg","caption":"","creditText":"Little, Brown and Company","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/ideas/","name":"Ideas"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/books/","name":"Books"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/4466139/power-of-when/","name":"Why You Should Pay Attention to Your Body’s Internal Clock"}}]},{"@context":"https://schema.org","@type":"VideoObject","name":"How Sleep Loss Affects Your Heart","description":"Sleeping for five hours a night alters your heart rate the next day","thumbnailUrl":"https://cdn.jwplayer.com/v2/media/EE7iJwKQ/poster.jpg?width=720","uploadDate":"2016-07-07T20:09:45.000Z","contentUrl":"https://cdn.jwplayer.com/manifests/EE7iJwKQ.m3u8","embedUrl":"https://time.com/4466139/power-of-when/","duration":"PT56S","potentialAction":{"@type":"SeekToAction","target":"https://time.com/4466139/power-of-when/?jw_start={seek_to_second_number}","startOffset-input":"required name=seek_to_second_number"}}] ```