The Science-Backed Health Benefits Of Sunlight + Vitamin D
After a long cold dreary winter, few things feel better than warm sunshine, longer lazier days, and the relaxed, cheerful, kick-back attitude that comes with summertime. As a functional medicine practitioner who often consults via webcam, I see this summer-loving attitude no matter where my patients live. But is it just a mood change, or are there actual, physiological benefits to the sunnier season? Actually, there really is science behind the benefits of summer. Let’s take a look:
Article continues below
Start Your Health Journey Today
FUNCTIONAL MEDICINE CONSULTATIONS FOR PEOPLE AROUND THE WORLD
The Health Benefits of Summertime
1. Sunlight cheers you up
Shorter, darker fall and winter days can lead to SAD or seasonal affective disorder, (1) a condition that affects about 6 percent of people severely, causing depression, and about 20 percent more mildly. SAD is four times more common in women, but fortunately it is alleviated by longer, sunnier days, come spring and summer. One mechanism for this is the brain’s ability to produce (2) more serotonin, that feel-good neurotransmitter, with increased exposure to sunlight. Full-spectrum lights can treat SAD during wintertime – ask your doctor about getting a prescription for these lights.
2. Seasonal food boosts your mood
All the best fruits and vegetables are fresh, ripe, and ready to eat during the warmer months and are much more likely to be available locally, through farmers markets and local farms or your very own backyard or porch garden. That means people tend to eat more produce in the summer, and therefore get more vitamins, minerals, and other phytonutrients that boost immune function and mood.
3. The sunshine vitamin feeds your brain
When your skin is exposed to sun, it starts synthesizing good ol’ vitamin D, the sunshine vitamin, which is responsible for the proper workings of hundreds of different pathways that control your mood, immune system, and brain function. Every single cell of your body needs vitamin D to do its best work, and there is no better time to bask in that vitamin producing sunshine than in the summer.
4. Nature calls
Nature heals, and that’s a fact. When it’s cold, people spend more time inside – another fact. But nature calls, and when you answer that call, you will feel better. One study published in the Proceedings of the National Academy of Sciences, demonstrated that when a group of people walked for 90 minutes in nature they reported fewer negative thoughts compared to the group who walked in the city. Functional MRI brain scans also revealed that the nature walkers had less activity in the subgenual prefrontal cortex, an area of the brain that plays a role in mood disorders and negative thoughts than the city walkers. So city folk, look for a park!
5. Fresh air fights viruses
Poorly ventilated rooms are more likely to foster (3) the cold virus, which also tends to spread more (4) during colder months. Other studies from the NIH found that the flu virus actually became tougher (5) during winter.
6. More sun means better sleep
The presence and absence of sunlight talks to your brain’s pineal gland, telling it to slow down the production of that sleepy-time hormone melatonin when it’s light, and increase production when it’s dark. When the dark hours are longer, and you are outside in the sunlight less often, it can be harder to wake up in the morning, and you may feel sleepier during the day. This can also leave you with less melatonin production at night, reducing sleep quality because your pineal gland isn’t getting those natural signals.
7. Genes adjust to the seasons
About 25% of your DNA actually changes with the seasons, according to one fascinating study (6) published in the scientific journal Nature. The study found that during the winter months, DNA changes seemed to be geared toward preparing for increased exposure to viruses. In the summer, different sets of genes were turned on that were more geared toward blood sugar balance, perhaps in anticipation of all that delicious summer produce. This summer change helps calm cravings and burn off winter fat, too.
8. Sun chills out over-reactive immune responses
Sunlight is sometimes used to treat auotimmune diseases of the skin, like psoriasis, because sun exposure can actually help suppress an overactive immune system. This may be because sun exposure increases white blood cells, which help fight disease and defend the body against infection.
Since you can’t stop winter from coming, does all this summer awesomeness mean you should move to a warm climate for an everlasting summer? Don’t get that one-way ticket to the tropics just yet. One study found that people were no happier in southern California than in the cold, cloudy, snowy, rainy Midwest, even though Midwesterners complained more about the weather.
Other studies point to the fact that while suicide rates are higher in the Arctic circle, they are actually even higher in warmer South Korea than in icy Scandinavian countries. Speaking of Scandinavians, they are listed as some of the happiest people in the world, despite their gloomy cold weather, comparatively. Must be all the hygge. Another factor may be the genetics of different populations, which could impact such biochemical functions as vitamin D metabolism. Another thing to consider is the diet of very happy people who live in colder, cloudier parts of the world, as traditional diets consist of a lot of wild-caught fatty fish – rich in vitamin D.
So do the seasons play a role in your mood, energy, and health? Absolutely, but they are far from the only factor, and are not nearly as important as dietary choices, activity level, family and social bonds, and attitude.
Your Guide For Boosting Vitamin D
Sometimes our lives get so busy that we forget to appreciate the wonders of the body and everything it allows us to do. You have 60,000 miles of blood vessels running through your body, and you produce 25 million new cells each second!
And while your trillions of cells all have their own purpose, they also have one thing in common: They all need vitamin D.
The sunshine vitamin
Vitamin D is known as the sunshine vitamin because our awesome bodies manufacture it when sunlight hits our skin. Your body absorbs sunlight using cholesterol, which helps convert sunlight into a form of vitamin D that your body can use. Sunlight is life to your body. And you might not guess it from its name, but vitamin D is actually more like a hormone than a vitamin. It helps to regulate hundreds of different pathways in your body. It is so important that vitamin D and your thyroid hormones are the only two hormones every cell needs, making them the king and queen of all hormones, and essential for good health including:
1. Fights depression
Have you ever noticed how sitting in the sun makes you feel good? The vitamin D activated by that sun exposure acts as an antidepressant in your system, which makes sense when you consider how many people get the “winter blues” coinciding with decreasing amounts of sunshine during the colder months. Low levels of vitamin D are linked to a 14 percent increase in depression and a 50 percent increase (7) in suicide rates! That makes this sunshine vitamin pretty essential!
2. Reduces asthma
Studies show (8) that pregnant moms with higher vitamin D intake give birth to babies with a 40 percent reduced risk of developing asthma. Other research suggests (9) that vitamin D has a protective effect against upper-respiratory infections in adults.
3. Balances immunity
Vitamin D is an integral part of your immune system, so it’s no surprise that low levels of vitamin D are associated with autoimmune conditions such as MS, (10) Parkinson’s, (11) type 1 diabetes, (12) inflammatory bowel disorders, (13) and autoimmune thyroid problems (like Hashimoto’s disease (14) and rheumatoid arthritis). (15) Conversely, optimal levels are linked with symptom improvement.
4. Strengthens bones
Just in case you haven’t heard, vitamin D prevents (16) the breakdown of bone and increases the strength of the skeletal system.
5. Boosts brain power
6. Fights cancer
People who have optimal vitamin D levels have lower levels of breast, (19) prostate, (20) colon, (21) ovarian, (22) and pancreatic (23) cancer. There is also some evidence that this vitamin can both kill cancer cells and impede their growth by up to 50 percent!
7. Improves fertility
8. Protects the heart
9. Calms inflammation
Inflammation is the common link between most chronic health problems, and vitamin D is an essential part of the body’s capability (28) to squelch the inflammatory storm going on.
10. Revs up metabolism
11. Enhances physical performance
Supplementing with this important vitamin has been shown to boost muscle strength and physical performance. Vitamin D has also been shown in some studies to increase balance, (31) decreasing falls by 20 percent.
12. Improves sleep
Sleep is so important for feeling and looking your best, and healthy levels of D are associated with (32) better sleep quality.
Ok, vitamin D is super important; so what can I do about it?
Here’s your new vitamin D-boosting lifestyle plan:
1. Test your vitamin D levels
In functional medicine, we aim for optimally healthy levels (not just within the lab’s reference range), which we consider to be somewhere between 60 and 80, depending on the person.
2. Get some sun
Spending some time out in the sun, about 20 to 60 minutes (depending on where you live in the world and your skin tone) without sunscreen is a great way to boost your D levels.
3. Eat more vitamin D-rich food
These are some of my favorites:
- Cod liver oil: 1 teaspoon: 440 IU (over 100 percent Daily Value)
- Sardines: 3 ounces: 164 IU (41 percent Daily Value)
- Salmon: 3 ounces: 400 IU (100 percent Daily Value)
- Mackerel: 3 ounces: 400 IU (100 percent Daily Value)
- Tuna: 3 ounces: 228 IU (57 percent Daily Value)
- Raw grass-fed milk: 1 cup: 98 IU (24 percent Daily Value)
- Caviar: 1 ounce: 33 IU (8 percent Daily Value)
- Organic eggs: 1 large: 41 IU (10 percent Daily Value)
- Mushrooms: 1 cup: 2 IU (1 percent Daily Value)
4. Supplement as needed
Since it’s difficult to get vitamin D exclusively through food, and most of us don’t spend enough time outside in the sun, supplementation may be necessary. Based on where your starting level is, I typically suggest supplementing with anywhere between 2,000 and 6,000 IU of vitamin D each day. Because vitamin D is a fat-soluble vitamin, I prefer the drops and capsules that include mct or coconut oil. Look for supplements without added fillers or colors, and retest every two or three months to ensure your levels don’t go too high, which isn’t good either.
5. Tap into vitamin synergy
When getting your vitamin D levels up to where they should be, it’s best to include the other fat-soluble vitamins: A, E, and K2. These vitamins are uber important in their own right and help balance out the vitamin D, making it more bioavailable but also preventing levels from getting too high. You can supplement with these, but I also suggest focusing on food jam-packed with these fat-soluble vitamins. Check out my article on the subject to learn more.
If you want to learn more about your own health case please check out our free health evaluation. We offer webcam as well as in-person consultations for people across the country and around the world.
- Seasonal Affective Disorder Am Fam Physician. 2000 Mar 1;61(5):1531-1532.
- Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD. Effect of sunlight and season on serotonin turnover in the brain. Lancet. 2002;360(9348):1840‐1842. doi:10.1016/s0140-6736(02)11737-5
- Temperature-dependent innate control of rhinovirus Ellen F. Foxman, James A. Storer, Megan E. Fitzgerald, Bethany R. Wasik, Lin Hou, Hongyu Zhao, Paul E. Turner, Anna Marie Pyle, Akiko Iwasaki Proceedings of the National Academy of Sciences Jan 2015, 112 (3) 827-832; DOI: 10.1073/pnas.1411030112
- Sun Y, Wang Z, Zhang Y, Sundell J. In China, students in crowded dormitories with a low ventilation rate have more common colds: evidence for airborne transmission. PLoS One. 2011;6(11):e27140. doi:10.1371/journal.pone.0027140
- Flu Virus Fortified In Colder Weather NIH March 10, 2008 https://www.nih.gov/news-events/nih-research-matters/flu-virus-fortified-colder-weather
- Dopico, X., Evangelou, M., Ferreira, R. et al. Widespread seasonal gene expression reveals annual differences in human immunity and physiology. Nat Commun 6, 7000 (2015). https://doi.org/10.1038/ncomms8000
- Umhau JC, George DT, Heaney RP, et al. Low vitamin D status and suicide: a case-control study of active duty military service members [published correction appears in PLoS One. 2013;8(9). doi:10.1371/annotation/9af84cbe-5576-4c4b-871c-f7ab0c64b9fd]. PLoS One. 2013;8(1):e51543. doi:10.1371/journal.pone.0051543
- Litonjua AA, Weiss ST. Is vitamin D deficiency to blame for the asthma epidemic?. J Allergy Clin Immunol. 2007;120(5):1031‐1035. doi:10.1016/j.jaci.2007.08.028
- Peter Bergman, Åsa U. Lindh, Linda Björkhem-Bergman, Jonatan D. Lindh Vitamin D and Respiratory Tract Infections: A Systematic Review and Meta-Analysis of Randomized Controlled Trials 2013. doi: 10.1371/journal.pone.0065835
- Simpson S Jr, Taylor B, Blizzard L, et al. Higher 25-hydroxyvitamin D is associated with lower relapse risk in multiple sclerosis. Ann Neurol. 2010;68(2):193‐203. doi:10.1002/ana.22043
- Knekt P, Kilkkinen A, Rissanen H, Marniemi J, Sääksjärvi K, Heliövaara M. Serum vitamin D and the risk of Parkinson disease. Arch Neurol. 2010;67(7):808‐811. doi:10.1001/archneurol.2010.120
- Dr Elina Hyppönen, PhD, Esa Läärä, MSc, Antti Reunanen, MD, Prof Marjo-Riitta Järvelin, MD, Suvi M Virtanen, MD Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study Volume 358, Issue 9292, P1500-1503, November 03, 2001. DOI:https://doi.org/10.1016/S0140-6736(01)06580-1
- Carter MJ, Lobo AJ, Travis SP; IBD Section, British Society of Gastroenterology. Guidelines for the management of inflammatory bowel disease in adults. Gut. 2004;53 Suppl 5(Suppl 5):V1‐V16. doi:10.1136/gut.2004.043372
- Alhuzaim ON, Aljohani N. Effect of vitamin d3 on untreated graves' disease with vitamin d deficiency. Clin Med Insights Case Rep. 2014;7:83‐85. Published 2014 Aug 13. doi:10.4137/CCRep.S13157
- Merlino LA, Curtis J, Mikuls TR, et al. Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women's Health Study. Arthritis Rheum. 2004;50(1):72‐77. doi:10.1002/art.11434
- Kato H, Ochiai-Shino H, Onodera S, Saito A, Shibahara T, Azuma T. Promoting effect of 1,25(OH)2 vitamin D3 in osteogenic differentiation from induced pluripotent stem cells to osteocyte-like cells. Open Biol. 2015;5(2):140201. doi:10.1098/rsob.140201
- Wilkins CH, Sheline YI, Roe CM, Birge SJ, Morris JC. Vitamin D deficiency is associated with low mood and worse cognitive performance in older adults. Am J Geriatr Psychiatry. 2006;14(12):1032‐1040. doi:10.1097/01.JGP.0000240986.74642.7c
- Buell JS, Dawson-Hughes B, Scott TM, et al. 25-Hydroxyvitamin D, dementia, and cerebrovascular pathology in elders receiving home services. Neurology. 2010;74(1):18‐26. doi:10.1212/WNL.0b013e3181beecb7
- Garland CF, Gorham ED, Mohr SB, et al. Vitamin D and prevention of breast cancer: pooled analysis. J Steroid Biochem Mol Biol. 2007;103(3-5):708‐711. doi:10.1016/j.jsbmb.2006.12.007
- Ahonen MH, Tenkanen L, Teppo L, Hakama M, Tuohimaa P. Prostate cancer risk and prediagnostic serum 25-hydroxyvitamin D levels (Finland). Cancer Causes Control. 2000;11(9):847‐852. doi:10.1023/a:1008923802001
- Gorham ED, Garland CF, Garland FC, et al. Optimal vitamin D status for colorectal cancer prevention: a quantitative meta analysis. Am J Prev Med. 2007;32(3):210‐216. doi:10.1016/j.amepre.2006.11.004
- Walentowicz-Sadłecka M, Sadłecki P, Walentowicz P, Grabiec M. Rola witaminy D w karcynogenezie raka piersi i raka jajnika [The role of vitamin D in the carcinogenesis of breast and ovarian cancer]. Ginekol Pol. 2013;84(4):305‐308. doi:10.17772/gp/1581
- Halcyon G. Skinner, Dominique S. Michaud, Edward Giovannucci, Walter C. Willett, Graham A. Colditz and Charles S. Fuchs, Vitamin D Intake and the Risk for Pancreatic Cancer in Two Cohort Studies Cancer Epidemiology, Biomarkers & Prevention September 2006. DOI: 10.1158/1055-9965.EPI-06-0206
- Martin Blomberg Jensen, John E. Nielsen, Anne Jørgensen, Ewa Rajpert-De Meyts, David Møbjerg Kristensen, Niels Jørgensen, Niels E. Skakkebaek, Anders Juul, Henrik Leffers, Vitamin D receptor and vitamin D metabolizing enzymes are expressed in the human male reproductive tract, Human Reproduction, Volume 25, Issue 5, May 2010, Pages 1303–1311, https://doi.org/10.1093/humrep/deq024
- Bodnar LM, Simhan HN. Vitamin D may be a link to black-white disparities in adverse birth outcomes. Obstet Gynecol Surv. 2010;65(4):273‐284. doi:10.1097/OGX.0b013e3181dbc55b
- Grimes DS, Hindle E, Dyer T. Sunlight, cholesterol and coronary heart disease. QJM. 1996;89(8):579‐589. doi:10.1093/qjmed/89.8.579
- Jared P Reis, Erin D Michos, Denise von Mühlen, Edgar R Miller, III, Differences in vitamin D status as a possible contributor to the racial disparity in peripheral arterial disease, The American Journal of Clinical Nutrition, Volume 88, Issue 6, December 2008, Pages 1469–1477, https://doi.org/10.3945/ajcn.2008.26447
- Adams JS, Hewison M. Unexpected actions of vitamin D: new perspectives on the regulation of innate and adaptive immunity. Nat Clin Pract Endocrinol Metab. 2008;4(2):80‐90. doi:10.1038/ncpendmet0716
- Salehpour A, Hosseinpanah F, Shidfar F, et al. A 12-week double-blind randomized clinical trial of vitamin D₃ supplementation on body fat mass in healthy overweight and obese women. Nutr J. 2012;11:78. Published 2012 Sep 22. doi:10.1186/1475-2891-11-78
- Earl S. Ford, MD, MPH, Umed A. Ajani, MBBS, MPH, Lisa C. McGuire, PHD, Simin Liu, MD, SCD, Concentrations of Serum Vitamin D and the Metabolic Syndrome Among U.S. Adults Diabetes Care 2005 May; 28(5): 1228-1230. doi:10.2337/diacare.28.5.1228
- Bischoff-Ferrari HA, Dawson-Hughes B, Willett WC, et al. Effect of vitamin D on falls: a meta-analysis. 2004. In: Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK70700/
- Grandner MA, Jackson N, Gerstner JR, Knutson KL. Sleep symptoms associated with intake of specific dietary nutrients. J Sleep Res. 2014;23(1):22‐34. doi:10.1111/jsr.12084
Shop This Article
Purchase personally curated supplements
and Dr. Will Cole’s books!
The information on this website has not been evaluated by the Food & Drug Administration or any other medical body. We do not aim to diagnose, treat, cure or prevent any illness or disease. Information is shared for educational purposes only. You must consult your doctor before acting on any content on this website, especially if you are pregnant, nursing, taking medication, or have a medical condition.
Our articles may include products that have been independently chosen and recommended by Dr. Will Cole and our editors. If you purchase something mentioned in this article, we may earn a small commission.
BY DR. WILL COLE
Dr. Will Cole, IFMCP, DNM, DC, leading functional medicine expert, consults people around the world via webcam and locally in Pittsburgh. He received his doctorate from Southern California University of Health Sciences and post doctorate education and training in functional medicine and clinical nutrition. He specializes in clinically researching underlying factors of chronic disease and customizing a functional medicine approach for thyroid issues, autoimmune conditions, hormonal imbalances, digestive disorders, and brain problems. Dr. Cole was named one of the top 50 functional medicine and integrative doctors in the nation and is the best selling author of Ketotarian and The Inflammation Spectrum.
Make Your Life a Cleanse
FUNCTIONAL MEDICINE GUIDES FOR GUT HEALTH, VIBRANT ENERGY + A CLEAN FOOD LIST
Get these FREE exclusive guides + access to subscriber-only giveaways, healthy recipes, and discount codes (including a 70% off code for courses!)