Our ancestors lived in tune with the natural light-dark cycle, and our bodies remain attuned to those rhythms. By understanding how light interacts with biology, we can make informed decisions about sun exposure, protection, and mitigating artificial light’s harmful effects.
Sunlight, which is part of the electromagnetic spectrum shown in Figure 1, is vital for regulating biological rhythms and supporting various bodily functions.
The sun’s light spans a broad spectrum, including ultraviolet (UV) radiation, visible light, and infrared radiation, each influencing the body in unique ways.
Despite the evolutionary significance of sunlight, modern human behaviors — such as the widespread use of sunscreen and sunglasses — have led to an unintended disruption of this natural process, with potential negative consequences for our health.
Figure 1.
This blog by Shepparton Podiatrist, Ryan Davey, delves into the fundamental role of native light frequencies from the sun; specifically UVB light and how it is utilised for the creation of vitamin D in the body.
This blog will explain the various functions of vitamin D, specifically examining its role in the:
- Musculoskeletal system
- Immune response
- Neurological health
It also explores why blocking sunlight, through the use of sunscreen or even indoor living, might be detrimental to health, and how these practices may hinder the body’s ability to produce the necessary quantities of vitamin D.
Then it offers practical recommendations for balanced sun exposure and mitigation of potentially harmful frequencies from indoor living and screen time.
Circadian rhythm
The circadian rhythm is your body’s natural 24-hour internal clock, influenced by light and dark cycles in the environment. This rhythm regulates essential biological processes such as sleep, hormone production, and metabolism, aligning them with the day-night cycle.
Sunlight plays a crucial role in resetting and maintaining this rhythm by signaling the brain to suppress melatonin (the sleep hormone) during the day and increase its release as night approaches.
In the modern world, many start their day by checking a phone or switching on the lights, followed by a commute to indoor, screen-based work under more artificial lighting. After work, we return home, cook and eat dinner under bright lights, and then often unwind in front of the television. This scenario does not allow for an accurate circadian rhythm to be maintained. This may be important for optimal health in ways we are only beginning to understand.
Figure 2.
Vitamin D: Bone Health, Immunity, and Brain Function
BONE HEALTH
Vitamin D plays a crucial role in keeping bones strong and healthy. It helps the body absorb calcium, which is essential for building and maintaining bone density. This prevents bone-related conditions like osteoporosis which can weaken bones, especially in older populations. By improving calcium absorption and supporting the natural process of bone repair, vitamin D helps lower the risk of fractures, thus improving falls outcomes which has been shown to be the largest contributor to hospitalisations among the elderly. A large scale research analysis revealed 35% of total hospitalisations of people 60 and over are due to falls. Some research papers report the rates could be as high as 60% in some populations.
IMMUNITY
Vitamin D also plays a critical role in the immune system by regulating inflammation and enhancing immune cell responses. It helps balance inflammatory processes, which is essential for preventing autoimmune diseases. Low vitamin D levels are linked to higher risks of infections and chronic inflammatory conditions like rheumatoid arthritis.
A study published in early 2022 displayed some striking results regarding vitamin D and severity of Covid19 infections. It was found that people who had above 20 ng/ml vitamin D had 14 times better outcomes in regard to severity and duration of illness. Vitamin D also had a significant impact on reported mortality rates across all demographics of people infected with COVID19.
BRAIN FUNCTION
In the brain, vitamin D receptors are present in regions governing mood, learning, and memory. Deficiencies have been linked to depression and neurodegenerative diseases. While supplementation can help, obtaining vitamin D naturally through sunlight is preferable. See figure 3 for reference on the major differences between the form derived from sunlight vs consumed through the digestive system.
Figure 3: Sunlight vitamin D vs Dietary vitamin D
If you have had general blood work done recently, or intend to have testing done, the normal range for vitamin D are:
- Sufficient levels: 50–125 nmol/L (20–50 ng/mL)
- Insufficient levels: 30–50 nmol/L (12–20 ng/mL)
- Deficient levels: Less than 30 nmol/L (less than 12 ng/mL)
Blocking Sunlight: The Impact of Sunscreen, Sunglasses, and Indoor Living
The use of sunscreen and sunglasses, though well-intentioned, inadvertently reduces vitamin D synthesis. Sunscreens contain active ingredients like avobenzone, oxybenzone, and octinoxate that block UVB rays. While sunscreen lowers the risk of US skin damage, excessive use—especially combined with limited natural sun exposure—can lead to vitamin D deficiency. Striking a balance between sun protection and vitamin D production is essential.
Furthermore, sunglasses block UV and blue light, altering the sunlight that reaches the retina. This means that although sunglasses are seen as eye protection, they can have a significant negative effect on the body’s circadian rhythm.
One proven function of the retina is regulation of the sleep-wake cycle. Blocking light during the day disrupts this balance, causing sleep disturbances and hormonal imbalances. This means that overusing sunglasses outdoors can have extensive unintended consequences.
See figure 4:
Understanding the Balance of Light
In contrast to sunlight, artificial blue light from LEDs, laptops, and smartphones disrupts circadian rhythms and melatonin production. Blue light overexposure, especially at night, suppresses melatonin (our sleep hormone), leading to insomnia, daytime fatigue, and increased risks of chronic diseases like obesity, type 2 diabetes, and cardiovascular issues.
Disrupted circadian rhythms impact metabolism and hormone levels, throwing off essential processes and contributing to chronic health problems. While sunlight supports our biology, the prevalence of artificial light at inappropriate times poses serious risks to health and longevity.
While sunlight is fundamental to human biology, artificial light—particularly blue light—presents significant challenges. Not all light is created equal. Sunlight provides essential light frequencies for vitamin D production, circadian rhythm regulation, and other physiological processes.
Practical Tips for Sunlight Exposure
Balancing your sun exposure and mitigating exposure to artificial light is undeniably important. This practice can also amplify other health practices in your current routine.
Balancing sun exposure while protecting against harm can optimize vitamin D levels and overall health. Here are practical strategies:
- Morning Sun Exposure: Aim for 30 minutes of unfiltered sunlight exposure in the morning to prime your skin and set your circadian rhythm.
- Consistent UV Light Exposure (10 am–4 pm): Start with 3×5 minute sessions, then progressively increase duration. Similar progressive overload principles can be applied to sun exposure just like training a muscle in the gym. Slow and steady increases win in the long run. Pay close attention to skin redness or tenderness as this will be important in finding your current limit and be more accurate with your sun exposure.
- Selective Sunscreen Use: Use hats, clothing, or natural sunscreens like zinc-based or beef tallow products when needed. Apply selectively to sun-sensitive areas (e.g., face and shoulders) rather than full-body use to balance protection with vitamin D synthesis.
- Limit Sunglasses: Avoid sunglasses in the morning to allow natural sunlight to regulate circadian rhythms. For glare protection, opt for lenses that allow more light transmission rather than a polarized lens which completely blocks certain important frequencies.
- Maximize Natural Light Indoors: Increase exposure to natural light by opening windows, curtains, and blinds. Position workspaces near windows to benefit from sunlight throughout the day.
- Protect Against Artificial Blue Light: Limit screen time in the evening and wear PPE such as blue-light-blocking glasses, particularly at night, to support accurate melatonin release and sleep quality. We recommend Block Blue light as a good place to source your glasses, as well as further information on improving your light environment. https://www.blockbluelight.com.au/?ref=RYANDAVEY
Summary
Sunlight is the primary source of vitamin D, responsible for 80-90% of production, while food provides only 10-20%.
Sunlight and vitamin D play an integral role in health and wellbeing, interacting with almost all bodily systems.
Excessive sunscreen use can hinder vitamin D synthesis, so strategic application is essential to balance protection with the proven health benefits of sun exposure.
Sunglasses block essential light frequencies that regulate circadian rhythms, potentially impacting sleep and hormonal balance.
Striking a balance between sun protection and exposure is crucial for optimizing vitamin D levels, sleep quality, and overall well-being.
By embracing the power of sunlight, you can unlock a vast array of health benefits and support your overall well-being. I’ve seen first hand, the profound impact this essential nutrient can have on all aspects of health. So, step outside, soak up some sun, and let your body reap the rewards of this natural, free source of energy and vitality. Your health will thank you.
References:
Dror, A. A., Morozov, N., Daoud, A., Namir, Y., Yakir, O., Shachar, Y., … & Sela, E. (2022). Pre-infection 25-hydroxyvitamin D3 levels and association with severity of COVID-19 illness. PLoS One, 17(2), e0263069.
Karlsson, M. K., Magnusson, H., von Schewelov, T. P., & Rosengren, B. E. (2013). Prevention of falls in the elderly—A review. Osteoporosis International, 24(3), 747–762. https://doi.org/10.1007/s00198-012-2256-7)
Images sourced from:
https://www.hukseflux.com/library/measuring-sunlight-what-instrument-to-use
https://astonrx.com/blogs/read/managing-your-circadian-rhythm
Ryan Davey
Podiatrist, Shepparton, GV Sportscare
We’re excited to now stock Tiny Treads at GV Sportscare!
Wide toe box to let little toes spread naturally
Need help finding the right size?
– Ryan Davey, Podiatrist, Shepparton
How can our Shepparton based Physiotherapists help with your postnatal return to running?
Most people are surprised to find that their physio or podiatrist is very keen to get them off crutches ASAP. In severe ankle sprains or suspected fractures, crutches are required, however in the mild to moderate ankle sprain crutches will actually slow down your recovery. Crutches reduce the weightbearing through the joint (which is a good thing if there is too much pain and damage). However in a mild to moderate injury it is unnecessary and will cause you to lose movement and strength, which you will need to work harder to regain as part of your rehab. Your Shepparton Physio or Podiatrist are able to assess your injury and guide you as to whether or not crutches are required and work with you to wean you off them!
The sooner you can be seen by your Podiatrist or Physio the better. When we waste a few days with the wrong management you are slowing down your recovery. Most people think injuries are a time based recovery, ie I have sustained a grade one ankle sprain therefore I will be back to sport in 2 weeks. This is partly true, injuries require healing and that takes time. However from our point of view your return to sport or activity is mostly based on ticking off certain criteria. For example can you raise onto your toes, can you stand on one leg, can you hop, can you run, etc. If you can’t do these things it doesn’t matter if your two weeks has passed, you are still not ready to return to activity. We then base our rehab on what you can and can’t do and aim to progress you on as quickly as possible. 
In the first 48-72 hours of your injury it is recommended to avoid anti inflammatories such as ibuprofen (Nurofen) and Voltaren. This is because the inflammation that occurs is your body’s response to injury and it actually brings 
One of the biggest risk factors for future ankle sprain is previous ankle sprain. While those with mild ankle sprains will likely manage to get back to sport, the issue we commonly see is that the injury has caused a loss of range of motion, strength, balance or coordination on that side. Therefore you can understand how even though you have returned to sport that these deficiencies can result in subsequent ankle sprains and more time away from the sport that you love! With simple assessment and exercises we can get you on track to work on these deficiencies and therefore reduce your risk of future ankle injury!
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