In this weeks post, we will be reviewing three recent studies that delve into the effects of morning light exposure on mood and behavior, whether the glycemic index of a food influences the impact of prolonged sitting on blood vessel function, and how passive heat therapy might be a useful tool to combat blood vessel dysfunction and cardiovascular disease.
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Our mood is heavily influenced by our environment. Light (from the sun) is a well-known regulator of mood and behavior in humans and animals. Our brain needs to receive light-dark cues in order to properly entrain our circadian rhythms to our environment, which allows a precise coupling of internal physiological processes with external events. An example of when this goes awry is seasonal affective disorder (properly acronymed SAD), a depressive-like state that emerges during long winter months and at northern latitudes, when sun exposure is extremely low. This illustrates the profound mood-boosting and cognition-enhancing effects that properly timed light exposure can have on health, and the adverse effects that can be wrought from a lack of exposure.
This study used a 30-minute period of morning light exposure (a “light pulse”) in mice (technically night light exposure, since mice are nocturnal) to demonstrate that light activates a specific circadian clock gene within the brain known as Period 1. Following the light exposure, mice demonstrated reduced despair behaviors, indicating that light may be beneficial for regulating mood and even depressive-like symptoms. Mice who had their Period 1 gene knocked out did not experience any beneficial effects of light exposure, implicating this clock gene in the beneficial effects of light on mood and behavior.
Application: Expose yourself to light first thing in the morning! This is known to have positive effects on mood, setting your circadian rhythm, and just helping you wake up! There is also some evidence that you should expose yourself (really your eyes) to light at different times throughout the day in order to keep providing your body with light and time cues. A morning, early-afternoon, and evening walk could be one of the best ways to leverage this biohack. Couple light exposure with some exercise and food for a more robust circadian effect.
Sitting is not the new smoking, as you may have read in some (misleading) news headlines. However, there is no doubt that too much sitting is probably not the best for health, since a high amount of sedentary behavior is associated with a wide range of metabolic and other diseases. Sit as little as you can, but don’t stress if your day job requires it. You can probably counteract sitting by engaging in moderate to high levels of physical activity and taking frequent walk breaks throughout the day.
Our cardiovascular system may be uniquely susceptible to the detrimental effects of sitting. Being immobile for a long period of time reduces blood flow throughout our body, which can cause vascular dysfunction in the legs, arms, and the brain and increase the stiffness of our arteries. Over time, this could expose one to a greater risk for cardiovascular complications. One thing that many people do while sitting is eat. For this reason, it would be beneficial to understand how prolonged sitting combined with a meal (particularly one that is high in sugar or simple carbohydrates, which are also known to be detrimental to vascular health) may influence blood vessel function.
This study investigated the combined effects of prolonged sitting and a high-glycemic-index (GI) meal on total body arterial stiffness. Young healthy adults were exposed to a 3-hour bout of sitting after consuming either a high- or a low-GI meal. The GI of a food refers to how a it affects blood sugar — with a high GI meal causing a more rapid and elevated blood glucose response. As you can see below in figure 2 from the study, the high-GI meal spiked blood sugar much more than the low-GI meal and was elevated throughout the sitting period until around 2 hours, when it dropped below the low-GI meal (sugar crash, anyone?)
Arterial stiffness was significantly increased after the prolonged sitting bout, however, the high- and low-GI meal had a similar response — meaning the high-GI meal was not any more detrimental than the low-GI meal to arterial stiffness.
Application: While this study was in young, healthy males and females, it indicates that eating a meal and sitting for a period of 3 hours is probably not great for our blood vessels. It doesn’t seem like the type of meal matters much in this case, since no differences were found between the high and low-GI meals. The takeaway here would be to never sit for more than 3 hours at a time (I would recommend no more than 30 minutes to 1 hour at a time), especially right after a meal. I’m a strong advocate for a post-meal walk of 15-20 minutes before I return to sedentary work, finding that this helps with my digestion, cognition, and overall energy levels.
Heat exposure (sauna, exercise in the heat, hot baths) is a great way to improve bodily health. There is an abundant literature on the effects of short-term and regular sauna use on cardiovascular health, with many of the effects “mimicking” those observed with exercise training — including reduced blood pressure, improved resting HR, and better vascular function and reduced arterial stiffness.
This begs the question of whether we can develop easy-to-implement strategies to improve vascular health and function in individuals who may be at risk for conditions like peripheral artery disease (PAD) and hypertension. Not everyone has access to a sauna, and lower-cost heat therapies might be a more feasible and easy way for individuals to access regular heat exposure.
This study investigated whether lower-limb heating could acutely improve markers of arm and leg vascular function and arterial stiffness in healthy young men and women.
Participants took part in two different heating conditions: one involving 45 minutes of ankle-level hot water immersion and another involving 45 minutes of knee-level hot water immersion. The temperature of the water was 45C, or 113F, which would be similar to a pretty warm hot tub.
In both heating conditions, arm vascular function was improved and leg arterial stiffness was reduced. Interestingly though, leg vascular function was not improved after heating, even though the legs were the limb being exposed to the hot water immersion. What this tells us is that the heat therapy is having system-wide benefits that are likely due to the release of certain inflammatory molecules. Indeed, it was also shown that a signaling molecule known as heat-shock protein (HSP) was elevated after knee-level hot water immersion. HSPs likely play a major beneficial role in the adaptations to any heat therapy, and also are implicated in the benefits of exercise.
Application: If you’re lucky enough to have access to a sauna, use it, OFTEN! If not, it seems like less intensive forms of heat therapy may also have cardiovascular benefits. Submerging yourself in a hot bath (though it likely won’t be nearly as hot as the water in this study), sitting in a hot tub, or using local heating such as in this study can all be effective forms of “thermal therapy.” If anything, a hot bath can help you unwind and destress, which has benefits for your physical and emotional health as well.
I hope you learned something interesting from at least one of these studies, and perhaps found something that you can take away and apply to your own life. See you next week!