Our bodies are deeply influenced by light and darkness, guided by an internal clock called the circadian rhythm. This 24-hour cycle helps synchronize our bodies with the day-night cycle, determining when we feel alert or sleepy. Acting as your body’s natural schedule, the circadian rhythm ensures you wake up and wind down at appropriate times. Light promotes energy and alertness, while darkness signals your body to prepare for rest. This is why we generally feel more awake during the day and ready for bed at night (1). Remarkably, nearly every organ, tissue, and cell has its own circadian rhythm, collectively attuned to the daily cycle of light and dark (12). 

How It Works 

When sunlight reaches your eyes, it activates photoreceptors in your brain. These light-sensitive cells trigger chemical changes that send electrical impulses to the suprachiasmatic nucleus (SCN), the master clock that regulates your sleep-wake cycle (2). This process resets your circadian rhythm, aligning it with the natural light-dark cycle (3). Sunlight exposure on the skin also facilitates the conversion of 7-dehydrocholesterol to the pre-vitamin form of vitamin D (4). This is significant because, in addition to helping regulate your internal clock, sunlight enhances your body’s ability to synthesize and utilize vitamin D. One key function of vitamin D is aiding in the production of melatonin, the hormone essential for sleep regulation (5). Notably, 8 out of 10 people with diabetes are suspected to have a vitamin D deficiency (6), which can make it more challenging to regulate sleep and synchronize the circadian rhythm effectively. 

Why Does It Matter? 

Our circadian rhythm regulates various bodily functions, including hormone levels, body temperature, digestion, mood, and energy (1). Disruptions to this rhythm, such as working night shifts or traveling across time zones, can cause fatigue, insomnia, irritability, and blood sugar or metabolic issues (13, 14). Supporting a healthy rhythm by soaking up natural morning sunlight and minimizing exposure to artificial blue light at night can help maintain balance (1, 7). Poor sleep is also linked to increased consumption of sugary foods, elevating the risk of developing Type 2 Diabetes. 

Improved Mood and Decreased Stress 

Exposure to natural sunlight not only boosts energy and aids in blood sugar management but also significantly improves mood and reduces stress. Sunlight triggers the release of serotonin, a hormone known for enhancing mood and fostering calmness and focus (8). 

Research shows that disruptions in circadian rhythms are linked to mood disorders, such as depression and anxiety (10). Regular exposure to sunlight can help regulate circadian rhythms, improving sleep quality and reducing symptoms of these conditions (9). Maintaining a consistent sleep-wake cycle and getting sufficient sunlight exposure can help stabilize mood and lower stress levels (11). 

Furthermore, sunlight is a vital source of vitamin D. Just 30 minutes of midday sun exposure can provide 10,000–20,000 IU of vitamin D, which is crucial for various bodily functions, including improving insulin sensitivity for better blood sugar regulation (4). 

Sunshine on a Cloudy Day 

Even on cloudy days, you can boost your mood and reduce stress using these sunlight-inspired strategies: 

• Pre- and Post-Shift Sunlight: If you work night shifts, aim for at least 20 minutes of sunlight exposure before and after your shifts. This can help your body synthesize vitamin D and support your circadian rhythm. 

• Maximize Daylight Hours: Spend time outside during daylight, particularly in the early morning when natural light is most effective at setting your circadian rhythm (15). Even on overcast days, diffused sunlight provides benefits. 

• Open Windows: Sitting by an open window with natural light can positively impact your mood and keep you connected to the outdoors, even if the sky is cloudy. 

• Use a Sun Lamp: A sun lamp can replicate natural sunlight and support your internal clock, especially in the morning or during seasons with limited daylight. 

• Consider Vitamin D Supplements: If sunlight is scarce due to weather or your work schedule, consult your healthcare provider about testing your vitamin D levels. Many people with indoor careers or living in less sunny regions require supplementation to maintain healthy levels. 

Sending Health Your Way!

The Tula Clinical Team

Austin MS, RDN, CSR, LDN, CD
Aubree RN, BSN