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Exposure to the sun gives us easy access to one of the most important vitamins for overall health. Unfortunately, with our modern fear of skin cancer, a growing number of folks—over a billion people worldwide1—are shying away from the sun. With an increasingly processed diet as well, many are not getting nearly enough of this crucial vitamin. Yet, with research discovering more and more vitamin D benefits each year, keeping up your levels is key to maintaining good health.
One of the best-known functions of vitamin D is helping the body absorb and utilize calcium (as well as phosphate, magnesium, and zinc), making it essential for developing strong bones and protecting you from osteoporosis as you age.2 But D does much more, by far. At least 1,000 different genes, governing nearly every tissue in the body—including several in the neuromuscular and immune systems—are thought to be regulated by 1,25-dihydroxyvitamin D, or D3, the active form. Vitamin D also plays a key role in preventing a host of health problems—such as heart disease, depression, autoimmune disorders, and even cancer—as well as regulating cell growth, supporting immune function, and reducing inflammation. It may even affect how easily you develop cavities.3,4
Deficiency: A Growing Epidemic
Despite how easy this nutrient is to acquire, a growing number of people have low vitamin D levels. This deficiency is associated with decreased bone health and chronic illnesses, including some cancers, multiple sclerosis, diabetes, and heart disease.
9 Most Common Symptoms of Low Vitamin D
- Blood-sugar issues
- Bone softening (low bone density) or fractures
- Joint pain (particularly in the back and knees)
- Low immunity
- Mood changes and irritability
- Muscle cramps and weakness
- Weight gain
Age and skin color are leading factors that can affect your body’s ability to produce adequate levels. Many cases of vitamin D deficiency occur in those living in areas of higher latitudes or who simply stay indoors. Additionally, deficiencies in minerals, especially magnesium, can contribute to low levels of vitamin D.
Also of concern is that as we get older, our ability to produce vitamin D in our skin decreases by 50%, making it even more important to increase either the time we spend in the sun and/or the amount of vitamin D we get from our diet or supplements. An age-related general reduction in kidney function negatively impacts the conversion of 25OH D to the active 1,25(OH)2 D, further decreasing our usable vitamin D levels.5 Regardless of your age, ensuring that your kidneys, liver and gut are all functioning optimally can help ensure your vitamin D levels remain at ideal levels.
Magnesium: A Codependent Relationship
Like many aspects of the human body, there are multiple moving parts and interconnected systems to consider. Magnesium and vitamin D definitely have a symbiotic relationship. For example, adequate levels of 1,25(OH)2D are required to maximize magnesium absorption, however, reduced levels of magnesium can hinder the conversion of vitamin D to its active form.
Magnesium itself plays a huge role in bone health, lowering your risk of osteoporosis, and in heart health. Unfortunately, industrialized agriculture and poor soil quality, the magnesium content in our food is estimated today at only 25% to 80% of pre-1950 levels. With our love of processed foods, as many as three-quarters of folks in the U.S. are magnesium-deficient.6
Maintaining ideal levels of magnesium is extremely important for not only ensuring your vitamin D levels remain in the ideal range, but for making sure the vitamin D you do have can do its job.6 The magnesium RDA for adults is 310-420 mg (depending on age and gender), and while you can supplement to help maintain healthy levels, plenty of Paleo-friendly foods contain high levels of magnesium. Some of the best dietary choices include leafy greens and fish, such as:
- 1 cup cooked spinach, 157 mg
- 1 oz pumpkin seeds, 156 mg
- 1 cup cooked beet greens, 98 mg
- 3 oz cooked halibut, 90 mg
- 1 cup cooked artichoke, 71 mg
Sun and Supplements
Spending time in the sun is the best way to increase vitamin D levels. There’s no danger of D levels getting too high, not to mention the other health benefits of being outside. To produce enough vitamin D to avoid becoming deficient, we should be spending at least 15-20 minutes per day in the sun, with enough bare skin exposed (think shorts and a t-shirt). It’s important that this time is spent without sunscreens, which block ultraviolet B waves (UVBs) and severely limit the skin’s ability to produce vitamin D.7
While sun exposure is ideal, depending on your health status, age, skin color, and where you live, you may need to supplement with vitamin D to maintain a healthy level. “For example in Boston, essentially no vitamin D3 can be produced in the skin from November through February.”7 Thanks to air pollution absorbing UVB radiation, living in big cities like Los Angeles can also negatively impact your ability to produce vitamin D from sunlight.
If you do decide to supplement, attain a baseline reading and regularly test your levels every couple months to understand how much you should be taking. Unfortunately there is no blanket recommendation for dosages, with suggested limits varying quite a bit. The Institute of Medicine suggests a safe upper limit of 4,000 IU per day, the Vitamin D Council recommends 5,000 IU per day, and the Endocrine Society Practice Guidelines states amounts as high as 10,000 IU per day are safe.
While rare, vitamin D toxicity can happen, but typically only by over-supplementing with megadoses of vitamin D, not from diet or sun exposure. Studies indicate that blood vitamin D levels above 100 ng/mL are excessive; above 150 ng/mL is considered toxic. This same study also shows that average daily intake of 10,000 to 15,000 IU per day “are not associated with deranged calcium or phosphate metabolism or toxicity.”8 Some experts suggest taking vitamin K2 alongside D, especially at high doses of D, because “vitamin D toxicity may cause blood vessel calcification, while vitamin K may help prevent this from happening.”9,10
If you suspect you are deficient in vitamin D, or if you want to find out, ask your doctor for a 25(OH)D test (also called 25-hydroxy vitamin D). This test is currently the most accurate way to measure the vitamin D level in your body. You can also order do-at-home vitamin D tests from folks like The Vitamin D Society or Ulta Lab Tests. Remember: Most health insurance carriers don’t classify vitamin D tests as “medically necessary”, and as a result, won’t cover these tests under their preventive care benefits.
The DMinder app, available for free in the App Store and Google Play, can be extremely helpful in helping you track the vitamin D you get from the sun. It helps you gauge the best time to be in the sun for maximum vitamin D, based on your location, body type, skin exposure, and time of day. It will also warn you when you need to get out of the sun before you burn, as well keep a running estimate of your vitamin D level. It’s a handy tool to help you track estimated levels between tests.
There’s no question that sustaining a healthy vitamin D level is key in maintaining optimum health. While there are certainly instances where supplementation is appropriate, be sure to test your levels first to get a baseline, then work with your doctor if necessary to move your levels into a healthy range. And don’t forget that when it comes to vitamin D, the sun is your best friend.
- Naeem Z. “Vitamin D Deficiency—An Ignored Epidemic.” Int J Health Sci (Qassim). 2010 Jan;4(1):V-VI.
- “Vitamin D: Fact Sheet for Health Professionals.” National Institutes of Health: Office of Dietary Supplements. 9 July 2019. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Gyll J, Ridell K, Öhlund I, Karlsland Åkeson P, Johansson I, Lif Holgerson P. “Vitamin D Status and Dental Caries in Healthy Swedish Children.” Nutrition J. 2018 Jan;17:11. doi: 10.1186/s12937-018-0318-1
- Schroth RJ, Rabbani R, Loewen G, Moffatt ME. “Vitamin D and Dental Caries in Children.” J Dent Res. 2016 95(2):173-9. doi: 10.1177/0022034515616335
- Gallagher JC. “Vitamin D and Aging.” Endocrinol Metab Clin North Am. 2013 Jun; 42(2):319-332. doi:10.1016/j.ecl.2013.02.004
- Uwitonze AM, Razzaque MS. “Role of Magnesium in Vitamin D Activation and Function.” J Am Osteopath Assoc. 2018;118(3):181-189. doi: 10.7556/jaoa.2018.037
- Wacker M, Holick MF. “Sunlight and Vitamin D: A Global Perspective for Health.” Dermatoendocrinol. 2013 Jan 1;5(1):51-108. doi: 10.4161/derm.24494
- Taylor PN, Davies JS. “A Review of the Growing Risk of Vitamin D Toxicity from Inappropriate Practice.” Brit J Clin Pharm. 2018 Jun 84(6):1121-7. doi:10.1111/bcp.13573
- Pérez-Barrios C, Hernández-Álvarez E, Blanco-Navarro I, Pérez-Sacristán B, Granado-Lorencio F. “Prevalence of Hypercalcemia Related to Hypervitaminosis D in Clinical Practice.” Clin Nutr. 2016 Dec 35(6):1354-8. doi: 10.1016/j.clnu.2016.02.017
- Arnarson A. “Is Vitamin D Harmful Without Vitamin K?” Healthline. 4 March 2017. https://www.healthline.com/nutrition/vitamin-d-and-vitamin-k#section3
- Cooley J. “10 Vitamin D Deficiency Symptoms You Can Identify Yourself.” University Health News Daily. 2 February 2019. https://universityhealthnews.com/daily/depression/10-vitamin-d-deficiency-symptoms-that-you-can-identify-yourself/
- Tello M. “Vitamin D: What’s The ‘Right’ Level?” Harvard Health Blog. 26 October 2018.