The Sunshine Vitamin
Whether we like it or not, winter is upon us. Can we rely on sunlight to get enough vitamin D during the winter months? The answer is, probably not! By learning to optimize our Vitamin D level year-round, we can support numerous health-promoting processes in the body.
The body makes previtamin D3 when our skin is exposed to ultraviolet-B (UVB) rays from the sun.1 Previtamin D3 is then converted in the liver to calcidiol (25 hydroxyvitamin D).1 Next, it heads to the kidneys for its final conversion to its most active form, calcitriol (1,25-dihydroxyvitamin D).1 Despite its name, vitamin D is actually not a vitamin, it's a hormone. And nearly every cell in the body has receptors for it.2
In the summer months, most people can produce sufficient vitamin D by exposing their skin to sunlight, with no sunscreen, for 10-15 minutes between 10 am and 2 pm when UVB rays are the strongest.3 Those with darker skin may need to be outside a bit longer since having higher amounts of the pigment melanin decreases vitamin D synthesis from sunlight.4 It's essential to balance getting enough sun that you can make vitamin D, with not getting so much that you develop redness or a sunburn.1 You want just enough to turn your skin slightly pink.3 Dr. Christiane Northrup, a women's health expert, recommends getting your sunlight around 10 am versus later in the day when the sun is at its hottest.4 There's no need to worry about getting too much vitamin D from the sun since the UVA rays will break down any excess.3
Sunlight is how we were designed to get most of our vitamin D. Sunlight is life for the body! But the plunging temperatures and the need to stay inside, combined with the lower position of the sun during the winter months, makes it hard to get enough UVB radiation for the body to produce sufficient Vitamin D. For most parts of the United States, Vitamin D made from sunlight exposure is minimal between November-February.5 Studies consistently show that Vitamin D levels tend to peak in September and are at the lowest in March.6 By optimizing our vitamin D production from the summertime UVB rays, we can carry some of it into the winter since its stored in our fat.3 Unfortunately, many of us spend our summer days working indoors and aren't able to get outside when the UVB rays are at their peak. Consequently, many people don't produce optimal amounts of vitamin D even during the summer months.
Benefits of Vitamin D
Vitamin D influences over 2,000 genes (about 10% of the human genome)!3 Without sufficient vitamin D, gene function may become impaired.4 It also supports healthy immunity, bone formation, glucose metabolism, and keeps our heart and skin healthy.3 If we are deficient in Vitamin D, our risk for many conditions increases, including; obesity, diabetes, hypertension, rheumatoid arthritis, fibromyalgia, chronic fatigue syndrome, osteoporosis, Alzheimer's disease, and some cancers.7
Got the Winter Blues? In addition to the conditions noted above, vitamin D also plays a significant role in supporting a healthy mood.3 If you notice yourself feeling more sluggish, irritable, down, or depressed in the winter, you're not alone. An estimated 25-35% of people have seasonal affective disorder (SAD) or some form of winter blues.8,9 This is often related to hormonal imbalances, and low vitamin D levels can play a role in this since it supports healthy hormone production.8
Test your vitamin D levels
To maintain optimal levels year-round, it's a good idea to have your vitamin D levels tested in the spring and the fall.3 You'll want to specifically ask to have a 25(OH)D test done, also called 25-hydroxyvitamin D.4 This is the primary circulating form of vitamin D and is widely used as a marker of a person's vitamin D status.10 Although health organizations have different goal ranges, ideally, you don't want a level below 30 ng/mL.7 The normal range is 30-100 ng/mL.2 Most experts recommend keeping your levels between 50-80 ng/mL.2 Physician-scientist, Dr. Sara Gottfried, suggests striving for 60-80 ng/mL to help dodge depression and prevent the winter blues.11
We are somewhat limited on our options for foods that are high in vitamin D since there are very few foods that naturally contain significant amounts. Seafood is the primary source of dietary vitamin D, but unless you eat a lot of it, often, it's not likely to be enough to meet your needs on its own. Some of the best food sources of vitamin D are cod liver oil, sardines, salmon, mackerel, tuna, egg yolks, and mushrooms.12
Adding Supplements to your Food and Sunshine
Since many people don't spend enough time outdoors in the sun, and it can be challenging to get vitamin D solely from food, it's often necessary to supplement. When using supplements, it's important to take the right form. Research has shown that supplementing with vitamin D3 (cholecalciferol), the active form, increases levels more effectively than vitamin D2 supplements.13 Dr. John Douillard, a leader in the field of natural health, recommends choosing vitamin D3 supplements derived from sheep lanolin due to this form being better absorbed.2 Strict vegans should look for a lichen-derived D3. To further improve absorption, take your vitamin D supplement along with a meal containing fat since it is a fat-soluble nutrient.14 Dr. Douillard also suggests taking vitamin D in the morning. This is due to science that has been done on circadian rhythms. We typically get vitamin D from the sun, and to help maintain a healthy circadian rhythm, we should take our vitamin D3 early in the day when possible.14
How much to take?
This will be based on your blood level, but for many people, a typical adult winter dosage is around 5,000 IU's daily.3 Summer dosages for adults are generally around 1,000-3,000 IU's daily.3 Functional medicine doctor, Mark Hyman, recommends if you have a deficiency, you may need a higher dose of 5,000-10,000 IU's for about 3 months.15 Once you've replenished your vitamin D stores, you can reduce to a maintenance dose of 2,000-4,000 IU's daily.15 Higher doses should be taken under a doctor's supervision. Always be sure to continue to monitor your blood level over time since vitamin D is a hormone, it fluctuates, and supplementation needs can change.
Did You Know?
Magnesium helps activate vitamin D. For vitamin D to become active in the body, you must have adequate magnesium on board.16 There is also an important synergy between vitamin D and vitamin K. They work together to optimize the flow of calcium through the body. Vitamin D3 enhances calcium absorption, and if we are deficient in vitamin K, calcium can build up and deposit into our soft tissues.17 Vitamin K2 plays a role in transporting calcium into the bones, where we want it! Dr. Ron Hunninghake, Chief Medical Officer of the Riordan Clinic, recommends that those taking 5,000-10,000 IU's of vitamin D daily should add 100 mcg of vitamin K2, in the mk7 form, to prevent unwanted calcification.18
*Those taking anticoagulant medications should not take vitamin K without first consulting with their healthcare professional.
As you can see, vitamin D and the nutrients that work together with it are essential for good health. Aim for optimal nutrient levels and watch your health improve!
1. Minich, Deanna. “The Synergy of Vitamins D and K: Finding Health in Balance.” Deanna Minich, 15 Dec. 2017,
2. Douillard, John, et al. “Vitamin D Benefits for Your Heart More.” John Douillard's LifeSpa, 30 Aug. 2019, https://lifespa.com/vitamin-d-heart/.
3. Douillard, John, et al. “Vitamin D Has Astonishing Health Benefits.” John Douillard's LifeSpa, 16 Dec. 2019,
4. Northrup, Christiane. “Why You Need Vitamin D.” Christiane Northrup, M.D., 21 Jan. 2019, https://www.drnorthrup.com/why-you-need-vitamin-d/.
5. Michels, Alexander, and Alexander Michels. “Can You Rely on Sunlight to Get Enough Vitamin D This Winter?” Linus Pauling Institute Blog, 27 July 2016, http://blogs.oregonstate.edu/linuspaulinginstitute/2016/01/25/sunlight-vitamin-d-winter
6. Kroll, Martin H., et al. “Temporal Relationship between Vitamin D Status and Parathyroid Hormone in the United States.” Plos One, vol. 10, no. 3, Apr. 2015, doi:10.1371/journal.pone.0118108.
7. Naeem, Zahid. “Vitamin d Deficiency- an Ignored Epidemic.” International Journal of Health Sciences, Qassim University, Kingdom of Saudi Arabia, Jan. 2010, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3068797/.
8. Cole, // by Dr. Will, et al. “How To Cheer Up Your Thyroid, Sex, And Adrenal Hormones During Winter.” Dr. Will Cole, 17 July 2019, https://drwillcole.com/winterproof-thyroid-sex-adrenal-hormones/.
9. Targum, Steven D, and Norman Rosenthal. “Seasonal Affective Disorder.” Psychiatry (Edgmont (Pa. : Township)), Matrix Medical Communications, May 2008, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2686645/.
10. Ganji V, Zhang X, Tangpricha V. Serum 25-hydroxyvitamin D concentrations and prevalence estimates of hypovitaminosis D in the U.S. population based on
assay-adjusted data. J Nutr. 2012;142(3):498-507.
11. Gottfried, Sara. Brain Body Diet: a 40-Day, Pill-Free Plan to Lose Weight, Boost Energy, and Eliminate Anxiety and Depression. HarperCollins Publishers, 2019.
12. “Office of Dietary Supplements - Vitamin D.” NIH Office of Dietary Supplements, U.S. Department of Health and Human Services,
13. Gottfried, Sara. “Vitamins D and K Go Hand-in-Hand.” Metagenics Institute, https://www.metagenicsinstitute.com/video/vitamin-d-and-k-video/.
14. Douillard, John, et al. “10 Reasons to Remember Your Vitamin D This Winter.” John Douillard's LifeSpa, 21 Jan. 2019, https://lifespa.com/10-reasons-take-vitamin-d-winter/.
15. Hyman, Mark. “The Sunshine Supplement: How To Beat A Vitamin D Deficiency.” The Chalkboard, 14 May 2019,
16. Uwitonze, Anne Marie, and Mohammed S. Razzaque. “Role of Magnesium in Vitamin D Activation and Function.” The Journal of the American Osteopathic Association, American Osteopathic Association, 1 Mar. 2018, https://jaoa.org/article.aspx?articleid=2673882&fbclid=IwAR1lfFxS15U94ic3BLivm9L VBNtCf8lKy5s-7BRxfO7HRRCiqPEqEA_yyAk.
17. van Ballegooijen, Adriana J, et al. “The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review.” International Journal of Endocrinology, Hindawi, 2017, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5613455/.
18. Hunninghake, Ron. “Vitamins D3 and K2 - The Dynamic Duo.” Riordan Clinic, 9 Oct. 2019, https://riordanclinic.org/2013/10/vitamins-d3-and-k2-the-dynamic-duo/