In the years since the pandemic reshaped daily life, mental health professionals around the world have documented a troubling trend: rates of stress, anxiety, and depression have risen significantly — and in many cases, they have not returned to pre-pandemic levels even as restrictions have lifted.
The reasons are complex. But one contributing factor is remarkably simple — and remarkably easy to address.
We are spending too much time indoors.
What Happens to Your Brain When You Stay Inside
The human body was not designed for the modern indoor lifestyle. For the vast majority of human history, people spent most of their waking hours outside — moving, working, and living under natural light. The brain, the endocrine system, and the immune system all evolved in an environment of regular sunlight exposure and daily physical movement.
When we deprive ourselves of these basic inputs — as millions of people did during pandemic lockdowns, and as many continue to do in the years since — the effects on mental health are direct and measurable.
The Endorphin Deficit
Exercise triggers the release of endorphins — the brain’s natural feel-good chemicals. Endorphins reduce the perception of pain, create feelings of euphoria and wellbeing, and help regulate mood and stress response. They are, in the most literal sense, the brain’s built-in antidepressant system.
When we stop exercising — as inevitably happens when we spend all day sitting indoors — endorphin production drops. The brain loses access to one of its primary mood-regulating mechanisms. Over time, this contributes to a baseline of low mood, irritability, and increased vulnerability to stress and depression.
The encouraging reality is that the endorphin response to exercise is dose-dependent and relatively rapid. Even a single 20-30 minute walk produces a measurable increase in endorphin levels and a corresponding improvement in mood. You do not need an intense workout to access these benefits — you simply need to move your body, preferably outside.
The Vitamin D Connection
The second major consequence of staying indoors is a reduction in Vitamin D levels — and the mental health implications of this are more significant than most people realize.
Vitamin D is unique among vitamins in that the body can produce it directly from sunlight exposure. When ultraviolet B rays from the sun hit the skin, they trigger a chemical reaction that converts a precursor molecule into Vitamin D3 — the active form that the body uses. Just 15-20 minutes of direct sun exposure on the arms and legs can produce a meaningful amount of Vitamin D in most people.
When sun exposure is reduced — as happens when people spend most of their time indoors — Vitamin D levels decline. And the consequences extend far beyond bone health, which is what Vitamin D is most commonly associated with.
Research has established a clear and consistent link between low Vitamin D levels and depression, anxiety, and seasonal affective disorder. Vitamin D receptors are found throughout the brain — including in regions involved in mood regulation, motivation, and stress response. When Vitamin D is deficient, these brain systems do not function optimally.
Seasonal Affective Disorder — No Longer Just a Winter Problem
Seasonal affective disorder — commonly known as SAD — was historically understood as a winter condition, triggered by the reduced daylight hours of the colder months. People in northern latitudes, who experience dramatically shorter days in winter, were most commonly affected.
But as Dr. Shintani has observed, the pandemic may have transformed seasonal affective disorder into a year-round phenomenon for many people. When individuals spend most of their time indoors regardless of the season — working from home, avoiding outdoor activities, spending leisure time in front of screens — they can develop the same Vitamin D deficiency and light deprivation that previously only occurred in winter.
The result is a form of depression that does not follow the traditional seasonal pattern — it simply persists, driven not by the time of year but by the indoor lifestyle.
The Simple Solution
The solution to this specific form of stress and depression is, as Dr. Shintani emphasizes, remarkably straightforward: get outside.
Going outdoors addresses both contributing factors simultaneously. Natural sunlight stimulates Vitamin D production, regulates circadian rhythms, and directly affects the brain’s serotonin system — another key mood-regulating neurotransmitter. Physical movement outdoors triggers endorphin release while also providing the additional benefits of fresh air, nature exposure, and a change of environment that all have documented positive effects on mental health.
Specific recommendations:
Aim for at least 20-30 minutes of outdoor time daily. Morning sunlight is particularly valuable — it helps regulate the circadian rhythm and sets the hormonal tone for the rest of the day.
Walk whenever possible. A daily walk — even a short one — provides both the endorphin benefits of exercise and the Vitamin D and mood benefits of natural light. Walking after meals, as discussed in previous articles, also provides blood sugar benefits.
Combine outdoor time with social connection. Walk with a friend, family member, or neighbor. Social connection has independent mental health benefits, and combining it with outdoor movement amplifies both.
Consider Vitamin D supplementation if outdoor time is limited. For those whose lifestyle, climate, or health situation genuinely limits sun exposure, a Vitamin D supplement can help maintain adequate levels. Most adults benefit from 2,000-4,000 IU of Vitamin D3 daily — though individual needs vary, and testing your levels with a simple blood test is the most accurate way to determine the right dose.
The Bigger Picture
Stress and depression are complex conditions with many contributing factors — including genetic predisposition, trauma, relationship difficulties, nutritional deficiencies, and underlying health conditions. For people experiencing significant mood symptoms, working with a qualified healthcare provider is important.
But the role of sunlight, movement, and Vitamin D in mental health is real, well-documented, and consistently underappreciated in conventional medicine. These are not alternative medicine claims — they are well-established physiological mechanisms supported by decades of research.
And unlike most pharmaceutical interventions for depression, going outside has no side effects, no cost, and no prescription required.
Dr. Shintani’s message is simple: your mental health needs sunlight and movement just as much as your body does. Step outside. Take a walk. Let the sun reach your skin.
Your brain was designed for this. Give it what it needs.
Dr. Terry Shintani is a Harvard-trained physician (MD, JD, MPH), a Living Treasure of Hawai’i, and the creator of the Waianae Diet and the Peace Diet. He continues to see patients at his Honolulu practice and shares daily health insights on YouTube.
🌿 Learn more at PeaceDiet.org | Watch the video: https://www.instagram.com/p/DawrTPgz7qt/
📖 Also read — Feeling Down or Stressed? Your Gut Flora Produces 90% of Your Serotonin: https://drshintani.com/wordpress/2026/07/12/feeling-down-or-stressed-your-gut-flora-produces-90-of-your-serotonin/