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Falling back on vitamin d

How the change of season affects your mood, health, and daily routines

Every day Apollo rides his fiery chariot across the sky with the sun in tow to bring the sun’s light to our planet that is ultimately the source of all life. Throughout history, the sun has been worshipped in one form or another by nearly every group of people. The ancient Greeks and Romans understood the vital importance of the sun in our lives, as Apollo was not just the sun god, but the god of medicine, healing, and youthful good health. But the ancients must have had a nuanced understanding of the sun because Apollo was also the god of plague – that is, Apollo, representing the sun, could bring both cure and disease. Likewise, scientists today have reached a similar dichotomous conclusion about the sun and how it affects our health. On the one hand, excessive sun exposure (for your skin type) can contribute to the formation of skin cancers due to the DNA-damaging effects of UVA radiation or cause sunburn via UVB radiation. Both types of radiation can damage collagen fibers in the skin causing loss of elasticity, and promote aging of the skin. These negative effects of ultraviolet radiation are relatively well-known due to large public health programs focused on the hazards of too much sun. The World Health Organization (WHO) measures the effects of disease in terms of disability-adjusted life years (DALYs) – which is just a measure of how many years of healthy life is lost in the entire world due to a certain disease or condition. WHO reported that in 2000 approximately 1.5 million DALYs[1] resulted from too much UV radiation from the sun, that could have been avoided if ultraviolet solar radiation was reduced to the appropriate amount for skin type. The “appropriate” amount is not, however, “no UVR exposure” [2] – sunlight is not in and of itself bad for you in any amount. In fact, that same WHO report estimated that zero exposure to sunlight would cause 3.3 billion DALYs per year, in what is likely even a low estimate given that many other probable links between the sun and health have long been suspected, but not yet definitively proven. In other words, too little sunlight would result in more than three orders of magnitude greater of a global disease burden than too much sunlight currently does.

Sunlight plays a major role in three areas that affect our health and vitality: disease states of the body, regulation of the body’s internal clock and our mental health (e.g. Seasonal Affective Disorder).

Vitamin D – The Sunshine Vitamin. When rays of light from the sun touch our skin, they set off a photochemical reaction that synthesizes large amounts of vitamin D. While vitamin D is found in a number of foods, these sources are insignificant compared to what we can get from even relatively short sun exposure. In fact, sunshine is the source of 80-100% of vitamin D.[3] Common food sources may have at most several hundred IU, which pales (or tans, as it were) in comparison to the 50,000 IU of vitamin D created by just 30 minutes in the summer sun in a bathing suit, for those with lightly pigmented skin.[4] (Even those with dark skin still synthesize large amounts, 8,000-10,000 IU under same circumstances). Spending just a few minutes outdoors in the sun can give your body more of the sunshine vitamin than you could ever consume through food. But in the winter, for those of us at higher latitudes (farther from the equator), the intensity of the sun’s light drops precipitously. Indeed, in the city of Boston, Massachusetts (42.2°N), a shocking study found that no previtamin D formed when human skin was exposed to sunlight on cloudless days from November through February. The story is even worse at Edmonton, Canada (52°N) where no vitamin D formed from October through March. [5]

Vitamin D and sunshine (their effects are hard to separate) play an outsize role in disease and keeping us healthy. Cedric F. Garland, a medical professor at the University of California, San Diego, claims that maintaining a sufficiently high level of vitamin D in the blood would slash the breast cancer rate in temperate areas by half, and that other cancers would be similarly decreased. He maintains this would be “the single most important action that could be taken by society to reduce the incidence of cancer in North America and Europe, beyond not smoking.”[6] A big claim indeed, and even if he’s only half right it’s one that should be explored, given all the evidence. Sunshine and vitamin D also prevent diseases of the bone, like rickets, osteomalacia and osteoporosis by helping us maintain adequate calcium levels and integrity of the skeleton. This was discovered over a hundred years ago, which is why rickets is no longer a disease we hear much about.

Ultraviolet radiation and Vitamin D also play a role in metabolic and heart health. Levels of vitamin D found in the blood were inversely correlated with blood glucose concentrations and insulin resistance[7] – i.e. the more vitamin D someone had the less likely they were to have problems associated with type 2 diabetes and proper insulin secretion – more vitamin D was associated with a more efficient metabolism, which has numerous benefits (see our Strength Training article – hyperlink). The sun may also likely help your heart and blood pressure. According to research done by Thomas Wang of the Harvard Medical School in the January 2008 issue of Circulation, the risk of hypertension (high blood pressure) is higher at higher latitudes, where people are exposed to less sunlight and consequently have lower vitamin D levels. Researchers found that directly after exposure to UVB radiation, like one gets from the sun, blood pressure drops.[8] Although the reasons why this is are not fully understood it is known that vitamin D plays a key role in downregulating the hormone renin in the kidneys, which regulates blood pressure indirectly by controlling water retention in the body. Finally, there is a seasonal pattern of incidence of and death from coronary heart disease – with peaks in the winter and troughs in the summer, suggesting the sun may play a role.

Ever think that you’re more likely to get sick in the winter? You’re not crazy. Vitamin D induces a polypeptide called cathelicidin that effectively combats both viral and bacterial infections.[9] This may explain the seasonality of many illnesses like the flu and cold-like illnesses – they occur more frequently in winter when people have lower vitamin d levels and effectively weaker immune systems. Of course, few things are this simple in the world, and this is likely to be one factor among many others (e.g. you spend more time inside around other people in winter, facilitating easier transfer of germs).

Circadian Rhythm – Your Body’s Internal Clock

The circadian rhythm is what regulates your body’s sleep and wake cycle – it’s why you get sleepy at certain times and why you may wake up at the same time every day. But like all clocks, our circadian rhythm needs to be regularly calibrated to make sure it’s running properly. Our body essentially checks our internal clock against a reliable external one – the sun. The emergence of light in the morning and the disappearance of it at night help to set our circadian rhythm. The body’s clock is set to the sun. As we sleep, our body responds to the total darkness by releasing the hormone melatonin, which makes us drowsy and keeps us asleep. As dawn comes our bodies sense the slowly increasing amount of sunlight, causing them to stop releasing sleep-inducing melatonin and to begin to release stimulating cortisol, causing us to wake up naturally, feeling refreshed and energetic. At least that’s what nature intended. This may have worked perfectly for much of humanity’s long existence, but in modern life we often sleep indoors in rooms that allow little morning sunlight in while also staying up late at night in front of glowing screens – making the body’s time keeping function more difficult. This problem is compounded in the winter, when the hours of daylight become even more scarce. As a result of little of the light of dawn reaching us in the morning, our body thinks it’s still night time and continues releasing melatonin, not the cortisol that would help us wake up naturally when our alarm rings. Likewise, at night time, we sit in front of the television, computer, cell phone and other devices that release light – the body senses the light and doesn’t release the melatonin that would help us feel pleasantly drowsy. This can lead to insomnia and delay the sleep cycle – making the issue of waking up in the morning more difficult. All this from a lack of natural sun light.

The circadian rhythm may also impact our mental health through a number of mechanisms. Serotonin is the precursor to melatonin, the former is produced during the day and the latter at night, typically. But in the winter or if one’s circadian rhythm is thrown off, as discussed above, melatonin may continue to be released in the morning or earlier at night. The more hours of total darkness, the more your body thinks it should be sleeping and the more melatonin it produces. The more melatonin it produces, crucially, the more serotonin it uses as substrate for the production. This means lower serotonin levels. Serotonin is associated with increase positive mood and decreased negative mood[10]. Lower serotonin levels may be experienced in the winter as a result of lower light levels and melatonin product, which might be one explanation for Seasonal Affective Disorder (SAD). SAD is a not uncommon condition where one experiences low mood and/or depressive in the winter months, and it is more common in countries at higher latitudes that receive very light sunlight in the winter.

Sunlight is great – how do I get more?

There are a few easy ways to get more sunlight and help restore the natural cycle of light exposure and reset our circadian rhythms, fighting Seasonal Affective Disorder. For starters, try not to always wear sunglasses outside, instead, going shades-free in the daylight, even for just 15-20 minutes, might confer significant health benefits. If you live in an area of the world that receives little sunlight, especially in the winter, or your living situation makes it difficult to maintain normal exposure levels (e.g. shift work) there are other options available. Light therapy is an old and well researched topic in medicine, useful for manipulating melatonin and serotonin levels, and by extension the circadian rhythm. You can use lamps that emit light equivalent to full day light – try putting one on your bedside table or at your desk to simulate dawn and help your circadian rhythm adjust – helping you wake up and feel energized, focused, and productive. Sun lamps may not be a day at the beach in the tropics, but they can help you survive the winter and get back to doing what you do best.

[1] Mead MN. Benefits of Sunlight: A Bright Spot for Human Health. Environmental Health Perspectives. 2008;116(4):A160-A167.

[2] 2006 World Health Organization (WHO) report The Global Burden of Disease Due to Ultraviolet Radiation. pg72

[3]Glerup, H. et al. Commonly recommended daily intake of vitamin D is not sufficient if sunlight exposure is limited. Journal of Internal Medicine. 247 (2): 260-268. (2000).

[4] Mead MN. Benefits of Sunlight: A Bright Spot for Human Health. Environmental Health Perspectives. 2008;116(4):A160-A167.

[5] Mead MN. Benefits of Sunlight: A Bright Spot for Human Health. Environmental Health Perspectives. 2008;116(4):A160-A167.

[6] ibid

[7] Lind, L. et al. Vitamin D is related to blood pressure and other cardiovascular risk factors in middle-aged men. American Journal of Hypertension. 8 (9): 894-901 (1995)

[8] Krause, R. et al. Ultraviolet B and blood pressure. Lancet. 352 (9129): 709-710 (1998).

[9] William Grant, director of the Sunlight, Nutrition, and Health Research Center, a research and education organization based in San Francisco

[10] Lansdowne, A.T. & Provost, S.C. Vitamin D3 enhances mood in healthy subjects during winter. Psychopharmacology. 135 (4): 319-323 (1998).

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