More Than Vitamin D

What sunlight does for sleep, mood, and the heart that a Vitamin D supplement can’t copy, and why never getting outside carries a cost of its own.

Last winter we wrote about vitamin D, and why a Canadian winter makes it so hard to come by. The sun sits too low from about October to March for skin to make any at all, so a Vitamin D supplement earns its place through our darkest months. This article picks up where that one left off, because vitamin D turns out to be of lesser importance to the story. Sunlight does several things for the body that no pill can match.

Here is the conversation that started us thinking about it. An aging parent is told, sensibly enough, to be careful in the sun. Careful becomes cautious, cautious becomes a hat and long sleeves, and somewhere along the way it turns into not going outside at all. A week goes by without fresh air. Then the other things start. Morning wake up slips later and later in the day. Mood dips. Small colds seem to arrive one after another and they linger. They doze off at three in the afternoon, then lie awake at midnight, and rise exhausted and in a low mood. None of these symptoms look like they have anything to do with the sun, so nobody connects them together.

The advice to avoid sunburn was never wrong. What went wrong is turning it into a single rule for everyone, applied without much regard for the patient who is standing in front of you. And the person it hurts most is the one already spending all day indoors: the home-bound older adult who now gets no daylight at all. This is worth understanding, because a good deal of the research pointing it out, is coming from inside mainstream medicine, not from its edges.

QUICK TAKE

•    Sunlight’s biggest benefits come from light reaching the eye and skin, and most of them can’t be replaced by a vitamin D pill.

•    Daylight sets the body’s clock. Without it, sleep, mood, and energy drift, a pattern easy to see in people who never get outside.

•    UV also releases nitric oxide from the skin, which relaxes blood vessels and gently lowers blood pressure, separate from vitamin D.

•    Sunburn and overexposure do cause skin cancer. The real problem is the "avoid-the-sun rule" applied to a sunbathing teenager and a housebound senior alike.

•    For an older adult getting no outdoor time, a little morning light is one of the safest, cheapest behavioural changes you can add.

Start with the points everyone agrees on

Too much sun causes skin cancer. That isn’t in dispute, and nothing here softens it. Ultraviolet light damages DNA in skin cells, sunburns raise the risk of melanoma, and years of overexposure add up to the more common skin cancers. Fair skin burns faster and carries more risk, so pale-skinned people have every reason to cover up at midday in July and to never let themselves burn. This is key. It’s the ground the rest of this article stands on.

The trouble isn’t the warning. It’s the magnitude of it. “Avoid the sun” got flattened into a rule that treats a nineteen-year-old frying at the beach and an eighty-five-year-old who hasn’t been outdoors in a week as the same person, with the same risk. They are not. And once you widen the lens from skin cancer alone to a person’s whole health, the math for that second person changes.

Daylight is the body’s clock

The most underrated thing sunlight does has nothing to do with vitamin D. Bright light entering the eye is the main signal that sets the body’s internal clock, the timer that runs sleep, alertness, mood, and the daily rhythm of hormones. That clock needs a strong dose of light, above all in the morning, to hold its schedule. And strong means stronger than most people imagine.

Indoor lighting feels bright, but it isn’t. A well-lit room measures a few hundred lux. An overcast day outside runs into the thousands. Open daylight reaches fifty to a hundred thousand. So an older adult sitting by a sunny window all day is still living in near darkness as far as their clock can tell. Starve that clock of morning light and you get the run of symptoms families describe without knowing the cause: sleep that drifts later, waking through the night, flat mood, low energy, more daytime dozing. It’s also why bright-light exposure is a recognized treatment for winter depression, and why it’s used in dementia care to settle sleep and ease evening agitation. A pill can’t do any of that. Only light can.

Indoors vs. outdoors

A well-lit room is a few hundred lux. A cloudy day outside is several thousand. Open daylight is 50,000 to 100,000. For the body’s clock, sitting indoors by a window is closer to darkness than to daylight.

What sunlight does that a pill can’t

Swallow a capsule and your blood level of vitamin D rises. That fact is what makes the rest of the story interesting, because when researchers gave people vitamin D in large trials, many of the benefits they expected from sunshine didn’t materialize. It started to look like blood vitamin D was partly a marker for how much sun someone got, and that sunlight was doing other useful things that a supplement wasn’t.

The clearest of these indicators appears in the skin. Ultraviolet light releases nitric oxide stored in the upper layers of the skin, and nitric oxide relaxes blood vessels, which brings blood pressure down. The effect is independent of vitamin D supplementation, it shows up within minutes of exposure in controlled studies, and it fits a long-known pattern: blood pressure and heart risk climb in winter and at higher latitudes, where sunlight is scarce. Regular, non-burning sun exposure is now tied to lower blood pressure and lower rates of heart disease and diabetes, most likely through this pathway.

Two cautions matter here. The effect is real but modest, more a gentle nudge than a treatment, and it is not a reason for anyone to change or skip their medication. If a client is on blood pressure pills, those pills stay as prescribed unless their doctor says otherwise. Daylight is something that supports the body alongside proper care, not a substitute for it.

Vitamin D supplementation modestly improves blood pressure. However, it can’t do what sunlight does for nitric oxide levels, blood pressure and circadian rhythms. You only get that by going outside.

The cost of a one-size rule

Put it together and a picture appears that blanket advice misses. Tell a whole population to avoid the sun and you will prevent some skin cancer, which is a real and worthy goal. But for the people already getting little or no sun, you may be trading a drop in one risk for a rise in bigger ones: worse sleep, lower mood, higher blood pressure, and the slow slide into a fully indoor life. Some of those problems then get managed with more prescriptions, which is how a person who mainly needed daylight ends up on a longer medication list.

This isn’t a fringe complaint. A dermatologist at a major university has spent years documenting the blood-pressure effect. A twenty-year study of nearly thirty thousand women, published in a mainstream medical journal, found sun avoidance behaving like a serious risk to survival, which we’ll unpack below. In 2025 a group of international researchers met and argued that the public message needs re-balancing, above all for people at low risk of skin cancer and high risk of getting no sun at all. The science is moving but the one size fits all advice, hasn’t caught up with yet.

HOW WELLURA HELPS

Getting an older adult a little daylight sounds simple, until someone has to make it happen every day. That’s work a Care Coordinator can build into a routine: a short walk or a sit on the porch in the morning, when the light does the most good, timed and properly dressed for the season, and kept sensible so there’s never a burn. For someone who hasn’t been outside in a week, even ten or fifteen minutes of morning light is a real change, and it costs nothing.

We coordinate it with the rest of the picture too, including looping in the person’s physician on anything that touches blood pressure, medication, or a history of skin cancer. The aim is steady daily light as part of good care, not one more project the family has to manage alone.

For the Curious

The study behind the longevity claims is worth understanding, caveats and all.

Researchers followed nearly thirty thousand Swedish women for twenty years and sorted them by sun-exposure habits. Those who avoided the sun had roughly twice the death rate of the group with the most exposure, with the middle group in between. Nonsmokers who avoided the sun had a life expectancy close to that of smokers who sought it out, which led the authors to describe sun avoidance as a risk to survival on a similar scale to smoking. The extra years among the sun-seekers came mostly from fewer deaths from heart disease and other non-cancer causes.

These results are observational, so part of the effect is probably reverse causation, with people who were already unwell staying indoors rather than staying indoors making them unwell. The women were fair-skinned Swedes at a northern latitude with modest background sun, so the numbers don’t transfer cleanly to sunnier places or to darker skin. And the sun-seekers did develop more skin cancer, though it tended to be caught with a better prognosis, and they still lived longer overall. Even with every caution attached, the result is hard to square with the idea that sunlight is always a hazard to be minimized.

The vitamin D angle rounds it out. Large supplement trials, including the big VITAL study, found that giving people vitamin D didn’t deliver many of the broad benefits that high sun exposure is linked to. One interpretation is that blood vitamin D was partly just a sign of a sun-rich life, and that the real work was being done by the other things sunlight impacts. Nitric oxide release from the skin is the best-characterized of those: first shown by the dermatologist Richard Weller and colleagues, later backed by blood-pressure studies published through the American Heart Association’s journal. None of this comes from outside medicine. It comes from within it, which is why it deserves a serious look.

SOURCES

Lindqvist, P.G., et al. “Avoidance of sun exposure as a risk factor for major causes of death.” Journal of Internal Medicine, 2016 (Melanoma in Southern Sweden / MISS cohort).

Weller, R.B. “Sunlight: Time for a Rethink?” Journal of Investigative Dermatology, 2024.

Liu, D., Feelisch, M., Weller, R.B., et al. On UVA-induced nitric oxide release and blood pressure (Southampton / Edinburgh), 2014, with follow-up work published via the American Heart Association.

Riedmann, et al. Expert meeting on the health benefits of sunlight beyond vitamin D, 2025.

Manson, J.E., et al. VITAL trial: vitamin D supplementation and disease outcomes. New England Journal of Medicine, 2019.

This article is for general information and isn’t medical advice. Sun tolerance, skin-cancer risk, and blood pressure are personal, so decisions about sun exposure or any medication belong with your doctor.