Welcome back to another edition of Midnight Shnack!
This was supposed to be the first issue of 2024 but alas, the holidays had me feeling a little extra lazy. And then school started… whoops. Today we are hitting the ground running - in the middle of a gloomy, rainy, cold, and rather strange winter - to talk about, maybe unsurprisingly, Vitamin D and Seasonal Affective Disorder (SAD). Why Vitamin D, specifically? Well, for those of you in my immediate circle, you have most definitely heard my mini rant about the importance of vitamin D… for the rest of you… here you go!
Today’s issue will be broken down into three main topics:
What is Seasonal Affective Disorder?
What does vitamin D have to do with this?
What is the function of vitamin D in the body?
Would you believe me if I told you that vitamin D can reduce, or in some instances, prevent the onset of depression?
Now, none of us are immune to the doom and gloom that we cycle through each winter season, but, there are some of us that seem to manage better than others. Take those who live in the beautiful sunny tropics, near warm sandy beaches - where the sun shines each day. Sure - the sun brings happiness, a sprinkle of joy, and an urge to frolic in fields of flowers - but besides its warmth and its beautiful rays cast across the sky, there lies an explanation as to why this is case. On the other hand, some people living in gross, dark, wet winters (in Vancouver for example) don’t feel the SAD effects as much as others.
My goal is to help you understand why. I want this issue to help you understand not only how this happens but most importantly, what you can do about it. If you take anything away from this, please let it be just how dang important vitamin D is. Look, I even bolded it so it must be super duper important. Anyways, let’s dive in shall we?
What is Seasonal Affective Disorder?
Simply put, SAD is a type of depression. We must be careful not to confuse it with feelings of sadness or anxiety brought on by stresses of the holidays, new year, and all the pressures that come with the change of season and new year.
What is new to me is that SAD can either emerge ahead of the fall and winter season or ahead of summer, following either a winter or summer pattern. It also has its own diagnostic criteria. Given the sudden increase in prevalence of SAD in the fall and winter seasons, it is currently hypothesized that chemical changes in your brain resulting from reduced sun exposure trigger the onset of SAD. This is why people living at increasingly northern latitudes experience SAD much more intensely than those living closer to the equator, where days are longer and there is more daylight.1
Why do we develop SAD?
There are three main hypotheses, including the one I mentioned above, as to why people experience SAD. First, research shows that people suffering from winter-pattern SAD have lower levels of serotonin, a hormone responsible for mood regulation and happiness. Why? Reduced sun exposure limits your body’s ability to synthesize vitamin D through your skin. Vitamin D is known to be a transcriptional regulator in the production of serotonin - meaning, if you don’t have enough vitamin D, your body can’t activate the synthesis of serotonin.2 Less serotonin means poor mood regulation. Second, there is a hypothesis that links melatonin to SAD. We naturally produce melatonin, a hormone that helps regulate sleep. During the winter season, a time when most mammals either migrate somewhere warm or hibernate (something us humans seriously need to embrace more fully), some individuals overproduce melatonin which leads to oversleeping, fatigue, and sleeping patterns that closely resemble hibernation.
Both serotonin and melatonin help maintain your daily rhythm and changes in these hormones disrupt this balance, affecting sleep, mood, and behaviour changes. As a result, it becomes increasingly difficult to adjust to seasonal changes.
Risk factors that elevate your likelihood of developing SAD include:
family history of Seasonal Affective Disorder
personal history of Depression or Bipolar Disorder
living far from the equator, either north or south (this does include Canada)
low production or low intake of Vitamin D
oh! and apparently being a woman?
This is where things get interesting… at least to me. Let’s talk about vitamin D.
What does Vitamin D have to do with SAD?
Everything. Almost.
Dare I say it is common knowledge that sun exposure helps you produce vitamin D, but I suppose what is less understood is that this produces nowhere near enough vitamin D to meet our daily needs, especially if you live far from the equator and experience darker, shorter days with limited sunlight. Even if you are exposed to sun on a regular basis, the angle at which the UV rays hit the surface of the earth affects how much vitamin D you will be able to produce.
This sunshine calendar helps you visualize sun exposure and vitamin D sufficiency depending on the month and latitude of your location. I love how 4 months out the year, us North American folk literally get no Vitamin D from sunlight. And we wonder why depression sky rockets during the winter months!
In all seriousness though, relying solely on the sun for vitamin D is not sufficient. And frankly, most people do not get enough from their diets either. 70% of the population does not meet their daily goal for vitamin D… just let that sink in. You’ll understand why this is important in just a second.
Now let’s add another layer. Melanin, a pigment compound found in skin (among other parts of the body), competes against the vitamin D synthesis pathway in skin for UVB rays from the sun. Individuals with a darker complexion have higher concentrations of melanin in their skin, which means they need more sun exposure to ensure they endogenously synthesize enough vitamin D.3
Endogenous Synthesis of Vitamin D ‘Normally,’ when we are exposed to UVB rays from the sun, a compound in our skin (7-dehydrocholesterol) absorbs them and is converted to vitamin D3. Several conditions must be met in order to synthesize adequate amounts of vitamin D. Factors such as season, time of day, latitude, altitude, air pollution, skin pigmentation, sunscreen use, and aging all affect how efficiently you can produce vitamin D.4 If you aren’t consuming enough and are unable to produce vitamin D3… well… that’s not ideal.
Serotonin Production Pathways As I mentioned above, vitamin D is an important transcriptional regulator in the production serotonin. Remember when I talked about epigenetics? That concept about having certain light switches flipped on or off depending on the nutrients you consume? Epigenetic’s explores how environmental and behavioural factors can cause reversible changes in our genetic expression.17 It’s like a light switch, where certain behaviours or environmental factors turn a gene on or off. In this case, low production or intake of vitamin D is in control of whether the serotonin production light switch is turned off, or left on to bring a little more light to your winter days. So, you best believe me when I (and all the research) tell you that vitamin D is fundamental to your overall mental wellbeing.
Now, I am not trying to minimize the complexity of depression and its effects on people. I hope this discussion, rather, has opened your eyes to another factor in this web of understanding why we may experience depressive episodes with the change of seasons. I would like to think it is abundantly clear but I suppose I will let you decide. Before you go though, there is one last topic to explore.
What is the function of Vitamin D in the body?
At this point, I would like to think that one critical function of vitamin D has become ever so apparent - its role in activating serotonin production, thus its role in SAD (and depression more generally).5 Numerous studies indicate that vitamin D has protective effects against depression for this reason. A meta-analysis reviewing observational and intervention-based research revealed that vitamin D supplementation (or increasing vitamin D intake through diet) was associated with reduced development of depression.6 So, what does this mean for you? Make sure you consume sufficient amounts of vitamin D. Especially in the winter when the sun is not shining. Two key takeaways for you:
the higher the levels of vitamin D stored in your body (below the safe upper limit of consumption), the lesser your risk of developing depression7
vitamin D supplementation appears to reduce symptoms and development of depression altogether
You do not have to supplement with vitamin D but it is not easy to get enough, especially if you follow a plant-based diet, don’t eat fish, or avoid dairy. Before we dive to much deeper, let’s take this back to the basics for a quick second. Here are some fast facts about Vitamin D that don’t need much elaboration:
Vitamin D is a fat-soluble vitamin meaning two things: its bioavailability increases (it is best absorbed) when you eat it with fat and excess vitamin D is stored in your body fat.8
The recommended daily allowance for vitamin D is 600 IU for adults over 18 years old (this is how much you should consume daily).9
Vitamin D is best paired with calcium, as vitamin D activates calcium absorption channels in the gut, increasing your absorption of calcium.
There are two ways you can get vitamin D: the UV rays from the sun stimulate a chemical reaction that synthesize vitamin D3 in your skin or you can get vitamin D2 from the food you eat (we have already covered this)
That’s all fine and dandy, but what exactly does vitamin D do? Besides, you know, help you manage depression? Or maybe prevent it altogether? Well! The list goes on!
Functions of Vitamin D in the Body Vitamin D is primarily responsible for bone health - it helps regulate the absorption of calcium and phosphorous and ensures the bone matrix is strong. As we know, vitamin D facilitates the production of neurotransmitters and hormones but it also more generally plays a role in neural signalling, supporting the transmission of messages between the brain and the body. Our B and T cells (cells that facilitate immune responses) have vitamin D receptors that help activate their function - this is a semi-complicated way of saying our immune system's ability to protect us from infection and illness depends on us getting enough vitamin D. Most notably, vitamin D has also been shown to have preventive power with respect to the development of certain cancers 🤯10 Absolutely crazy. If you are interested in a more comprehensive list, check out the Vitamin D factsheet.
Implication in Disease Given its diverse roles throughout the body, it becomes quite easy to see just how important vitamin D really is. For this reason, vitamin D has been implicated in a variety of diseases including depression, bipolar disorder, schizophrenia, cardiovascular disease, osteoporosis, cancer, type 2 diabetes, multiple sclerosis, autoimmune disorders, dementia, obesity, high blood pressure, arthritis, irritable bowel syndrome… um… COVID.1112 The list keeps going. Non-communicable diseases (NCD) are responsible for nearly 74% of deaths in North America.13 Now, correlation does not automatically imply causation folks but it is interesting to note the increasing prevalence of NCDs and the apparent vitamin D deficiency among our North American populations. Anywho! Just some food for thought.
I think I will leave here for today but if you are interested in an example of vitamin D’s effects on disease outcomes, go ahead and give this paper a read: Diet and lifestyle influences on risk of coronary heart disease. This paper explores a variety of nutrients and their role in coronary heart disease, but also explores the role of vitamin D.
Thanks for shnackin’ with me!
That is pretty much it from me today (unless you are a paid subscriber - there will be more to come. I know this was a lot to digest but I hope it’s got you thinking more about how profound the impacts of (in)sufficient intake of vitamin D is on our overall health. Whether it is safe sun exposure or consuming vitamin D rich foods, this speaks volumes as to why you should care about getting enough!
I would love to know what you took away from this post - feel free to leave a comment, question, you name it. It brings me so much joy to read through what you have learned! Oh! And remember, shnacks are always better when you share them 😉
https://www.nimh.nih.gov/health/publications/seasonal-affective-disorder#:~:text=In%20most%20cases%2C%20SAD%20begins,daylight%20hours%20in%20the%20winter.
https://pubmed.ncbi.nlm.nih.gov/25713056/#:~:text=Brain%20serotonin%20is%20synthesized%20from,serotonin%20synthesis%20is%20not%20optimal.
https://www.health.harvard.edu/staying-healthy/6-things-you-should-know-about-vitamin-d#:~:text=Melanin%20is%20the%20substance%20in,Weight.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897598/#:~:text=During%20exposure%20to%20sunlight%207,which%20have%20unique%20biologic%20properties.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908269/
https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/vitamin-d-fact-sheet#:~:text=Higher%20vitamin%20D%20levels%20have,cancers%20(14%E2%80%9317).
https://www.hsph.harvard.edu/nutritionsource/vitamin-d/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5440113/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9299393/#:~:text=Overview%20of%20NCDs%20in%20the%20Americas&text=Cardiovascular%20diseases%20were%20the%20leading,284%20049%20deaths)%20in%202019.