Are you up and out early in the morning? Or do you sleep in?

Natural sunshine has a powerful effect on several aspects of your health

You have most likely heard that sunlight is beneficial in improving mood as well as providing vitamin D. Now there is new evidence to suggest that sunlight can aid in weight loss as well. A recent study conducted at Northwestern University examined the effects of light exposure early in the day on Body Mass Index (BMI). How exactly did they make this connection? Read on to learn more about how sunlight can benefit your weight loss efforts.


The study included 54 participants with a mean age of 30 years. The participants wore a wrist monitor to measure light exposure and sleep patterns for 7 days in normal living conditions. They also kept food logs in order to monitor their caloric intake.

Background information included in the study referred to sunlight as having powerful biological signals that could represent a potential modifiable risk factor. The modifiable risk factor here refers to sunlight exposure with regard to duration, timing and intensity. The reason it is called a modifiable risk factor is because it can be modified for improvement in accordance with a specific recommendation in order to gain health benefits that may be associated with it.

Therefore, researchers suggest that modifying your sun exposure along appropriate duration, timing and intensity guidelines will aid in weight loss. The final conclusion of the researchers was that those exposed to sunlight early in the day had a lower BMI than those exposed to sunlight later in the day.

In this study sunlight was measured in lux. It was determined that outdoor light, even on cloudy days, typically has more than 1000 lux. Conversely, room light is only 150 – 500 lux – this is a significant difference from outdoor light! The study determined that participants who were exposed to daylight above 500 lux early in the day had lower BMIs. However, those who were exposed to daylight later in the day had higher BMIs.

Furthermore, the researchers came to the conclusion that in order to reap the benefits of sunlight with regards to weight loss, individual should expose themselves for 20 to 30 minutes per day between the hours of 8am – 12pm. It’s also important to note that the effects of sunlight on BMI were independent of physical activity level, caloric intake, sleep patterns, age or season. Sunlight, therefore, accounted for 20% of BMI.

Morning sunlight weight loss - morning run

The specific body mechanism affected by sunlight that was cited in the study to explain the findings is the circadian rhythm system. Circadian rhythm refers to the body’s internal clock. Your internal clock regulates your 24-hour cycle of biological processes. Some of the biological processes regulated by circadian rhythm are brain wave activities, hormone production, and cell regeneration. Metabolism and energy balance are also largely regulated by circadian rhythm. Circadian rhythm is what determines your sleep-wake cycles and these cycles are regulated and synchronized with light-dark cycles over a 24-hour time period.

Light is the most important influence and regulator of circadian rhythm and consequently metabolism. This explains why early light has a greater impact on BMI than light later in the day. Researchers also suggested that as a result of these findings those who are morning people would benefit more than those who are night people. Morning people rise earlier in the morning, either before or within the hours of 8am – 12pm to be able to experience the benefits of early light. Night people, on the other hand, tend to go to sleep later at night causing them to wake up later in the day, resulting in decreased optimal exposure to early light hours.

If you are interested in weight loss and lowering your BMI, it might be time to rethink how early you get up and out in the morning. Just 20 to 30 minutes of daylight early in the day, even on cloudy days can enhance your weight loss efforts.

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