Sunlight does far more than help your body make vitamin D. In this Quick Hits episode, Gerardo "Guti" Gutierrez explains how UVB, UVA, infrared, and blue light send different signals to the body, and how those signals can affect sleep, mood, metabolism, and hormones. For midlife women living mostly indoors or in northern climates, what kind of light you get, and when, may matter more than you think.

Most of us have been taught to think about sunlight in one of two ways. Either we avoid it because we're afraid of skin damage, or we assume a vitamin D supplement has the whole thing covered. In this Quick Hits episode, I revisit my conversation with Gerardo "Guti" Gutierrez , and he makes a compelling case that light is a much bigger piece of the hormone health puzzle than most women realize.

Here's the core idea. Different types of light, including UVA, UVB, visible light, and infrared, each interact with the body differently. UVB is what allows your skin to produce vitamin D. Morning light helps set your circadian rhythm, the internal clock that governs sleep, energy, and hormone release. Bright light at night can work against that same clock. When most of your day is spent indoors under artificial lighting, you may be getting the wrong signals at the wrong times.

This matters in perimenopause and menopause because so many of the symptoms women struggle with, including poor sleep, low mood, fatigue, and stubborn metabolic changes, are already tied to shifting hormones. Guti and I talk about how light exposure may be one more factor influencing those systems, why people in northern climates like Canada may get very little UVB for months at a time, and how red light therapy and UVB light therapy are not the same thing.

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In This Episode, We Discuss

• The difference between UVA, UVB, visible light, and infrared light
• Why UVB is necessary for vitamin D production in the skin
• Why sunlight and a vitamin D supplement are not exactly the same thing
• Why Canadians and others in northern climates may get very little UVB in winter
• How morning sunlight supports your circadian rhythm
• Why bright artificial light at night can interfere with sleep
• The connection between sunlight, mood, metabolism, and hormone signaling
• How red and near-infrared light interact with mitochondria
• Red light therapy vs. UVB light therapy
• Why timing, wavelength, and light exposure matter
• Guti's personal experience raising his testosterone through sunlight, exercise, and sleep

Key Takeaways

• Sunlight is several signals, not one. UVA, UVB, visible light, and infrared each affect the body differently.
• UVB is the vitamin D wavelength. Without UVB reaching your skin, your body can't make vitamin D from sunlight.
• Northern winters mean little UVB. If you live in Canada or another northern region, you may get almost none for months of the year.
• Morning light helps set your body clock. Getting outside early in the day supports your circadian rhythm, which influences sleep and hormone timing.
• Night light works against sleep. Bright artificial light in the evening may make it harder to wind down.
• Red light and UVB aren't interchangeable. Red and near-infrared light act on mitochondria; UVB drives vitamin D production.
• More UV isn't better. Timing and dose matter, and excess exposure carries real skin risks.

Frequently Asked Questions

Does sunlight do anything a vitamin D supplement doesn't?

According to Guti, yes. Sunlight delivers several signals beyond vitamin D. A supplement can raise your vitamin D level, but it doesn't provide morning light for your circadian rhythm or infrared light's effects on tissue. That doesn't mean supplements are unnecessary. For many women, especially in northern climates, supplementation is an important way to maintain adequate levels. The practical approach is to think of daylight and supplementation as working together, and to test your levels with your healthcare provider rather than guessing.

Can you make vitamin D from the sun in winter in Canada?

For much of the winter, most Canadians get very little UVB from sunlight. When the sun sits low in the sky, the UVB needed for vitamin D production is largely filtered out by the atmosphere, even on clear days. How long this "vitamin D winter" lasts depends on latitude. This is one reason vitamin D testing and supplementation are commonly discussed for people living in northern regions.

How does morning sunlight help with sleep?

Morning light helps set your circadian rhythm, which tells your body when to feel alert and when to wind down for sleep. Bright light early in the day signals that it's daytime, which helps your body time sleep-related hormones later in the evening. For women in perimenopause who are already struggling with sleep, a regular morning light habit is a simple, low-cost place to start, though it won't resolve sleep problems driven by hormone changes on its own.

Is red light therapy the same as UVB light therapy?

No. Red and near-infrared light do not produce vitamin D. Red light therapy uses longer wavelengths that Guti explains interact with the mitochondria in your cells. UVB is the shorter wavelength that triggers vitamin D production in the skin. Some devices combine both, but the two do different jobs. If you're considering a light device, check which wavelengths it actually emits and follow the manufacturer's safety instructions.

Can light exposure affect hormones in menopause?

Light exposure may influence hormone signaling, largely through its effects on the circadian rhythm, which helps regulate when many hormones are released. Guti discusses connections between sunlight, mood, metabolism, and hormones, though much of this research is still emerging. Light is best seen as one supportive factor alongside sleep, nutrition, exercise, and, where appropriate, hormone therapy, not as a replacement for medical care.

Is it safe to get more sun for vitamin D?

Sun exposure carries both benefits and risks. Excess UV exposure can cause sunburn, premature skin aging, and increase skin cancer risk. The right amount depends on your skin type, location, time of year, and personal and family history of skin cancer. Follow sun-safety guidance, avoid burning, and talk to your healthcare provider about vitamin D testing if you're concerned about your levels.

Disclaimer: This episode is for educational purposes only and is not medical advice. Excessive UV exposure can cause sunburn, premature skin aging, and increase skin cancer risk. Follow appropriate sun-safety guidance and device instructions.

About Gerardo "Guti" Gutiérrez

Gerardo "Guti" Gutiérrez is the founder and CEO of MitoLux, a Dallas-based company that makes home-use light therapy devices combining UVB, red, and near-infrared light. His background is in professional photography, where he spent more than 20 years working with light before turning his attention to photobiology, the study of how light affects living things.

In 2020, while dealing with chronic fatigue and a difficult period in his life, Guti began getting direct morning sun every day. That experience led him into years of reading research on sunlight and health, which he later wrote about in his book, Rewired by Light. He has since spoken on numerous health podcasts about UVB, vitamin D, circadian rhythm, and red light therapy.