How Light Affects Us

Our exposure to light has a profound effect our health, sleep and mood. The time we are exposed to light and the type of light we see affects how our minds and bodies work. Nature has designed us to function optimally when we are exposed to high light levels in the day and low light levels in the evening. Natural (ambient) sunlight is the most healthy source of light as it is stronger and brighter than other light sources (emitting up to 120,000 lux) and occurs at the right times of the day. Generally speaking, the more light we receive in the day (particularly early on in the day), the more of the sleep-promoting hormone melatonin we produce at night. As humans, we want to feel awake, alert and energised during the day; consequently, nature has enabled us to achieve exactly that. Indeed, exposure to bright light leads to the activation of the suprachiasmatic nucleus of the hypothalamus which instructs the pineal gland to limit melatonin production (perking us up). As light levels fade later on in the day, melatonin levels increase enabling us to relax and prepare for sleep.  

Melatonin Imbalance If production or non-production of melatonin occurs at the wrong time of the day (e.g., due to exposure to bright light late in the evening), negative biological and psychological effects can occur. The most common negative effects involve difficulty getting to sleep, daytime fatigue, subdued mood, increased blood pressure, raised blood glucose, lowered immunity and memory problems. In the long-term, disrupted melatonin levels have been linked to an increased of risk of type 2 diabetes, hypertension and cancer. In a minority of people, increased melatonin production can activate an affective (mood) episode such as a major depressive episode or manic episode.  

Do I Have Seasonal Affective Disorder (SAD)?

As the UK transitions into its autumn and winter months, most of its residents will start producing more melatonin during the day due to fewer daylight hours. In practical terms, this means that most of us will notice they are feeling more sleepy in the early evening and more lethargic during the day. For the majority of people, these changes occur “normally” and are not indicative of an affective disorder.  

However, a small minority of people do develop major depressive episodes in response to changing of the seasons; technically, this is referred to as Major Depressive Disorder With Seasonal Pattern, although the condition is popularly referred to as Seasonal Affective Disorder (SAD). Around 7% of UK adults are diagnosable of the clinical condition major depressive disorder. However, of those, only a small proportion develop symptoms during changing of the seasons (i.e., SAD).  

So how do we know if we have an affective disorder? In order to identify the presence of major depressive disorder, set diagnostic criteria must be met. This involves identification of five or more core symptoms of depression (including depressed mood or marked loss of interest) which are persistently present for most days for at least two weeks. Various other criteria must also be met (e.g., exclusion of a medical condition or use of substance that may account for the depressive symptoms). As specific symptoms need to be identified and deemed clinically significant for diagnosis, deciding if somebody has major depression is best determined by a trained mental heath professional.

If you are concerned you are suffering with major depression, you can arrange an assessment consultation with Equanimity Psychological Services (EPS) via email or webform; your clinician will able to inform you if you meet criteria of any clinical conditions and, if appropriate, outline suitable treatment options.  

So How Can I Remain Healthy During Autumn And Winter Months?

For many, a few simple lifestyle changes during the autumn and winter months will be enough to prevent common symptoms such as daytime tiredness and insomnia.   It is important to spend an hour or more every day outside to receive adequate (ambient) sunlight exposure. Even on an overcast winter day, the sun can emit up to 2,000 lux (which is around 8 times brighter than an average electrical light). Relying on electrical light during the day will lead to low melatonin levels during the evening and nighttime.  

To encourage healthy sleep, it is important to turn off electronic devices and dim the lights about an hour before bed. Leaving the lights on before bedtime will tell your body to perk up rather than wind down. If it is hard to avoid light during the evening, blocking out blue light may be an alternative. You can do this by purchasing glasses that block out blue light which are available from places like Amazon. Some software programs can also lower blue light computer emissions.  

For some people, using a light box during the autumn and winter is beneficial. People with SAD frequently benefit from daily light therapy sessions – particularly if they tend to oversleep and overeat. Similarly, those who work in dimly lit workspaces and those who experience a lack of energy and morning grogginess in the autumn and winter months may also benefit from daily light therapy. If you would like further information about light therapy and how it may help you, I recommend you read Robert J. Hedaya’s article “Light Therapy and Your Mental Health” which is available at: https://www.psychologytoday.com/blog/health-matters/201110/light-therapy-and-your-mental-health  

By Thomas Brown MBPsS

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