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  • Writer's pictureStacie Haaga

The Sunshine Vitamin: Vitamin D

I love an excuse to spend time in the sun.... and vitamin D is a great excuse!

Although we call it a fat-soluble vitamin, this "sunshine vitamin" actually acts more like a hormone in the body. It is considered to be a prohormone, meaning that it is a precursor to a hormone, called 1,25-D, which helps the body to make its own steroids, such as cholesterol, a substance necessary to the integrity of every cell in the body.

Among its many other functions and benefits, Vitamin D regulates gene expression, keeps calcium and phosphorus levels in check for healthy bones, improves mood, improves heart function, supports weight loss, and above all, it ensures that the immune system functions properly.

Vitamin D Deficiency

Vitamin D deficiency is very common: approximately 41% of men and 53% of women in the United States have levels of 25(OH)D below 28 ng/ml (70 nmol/L) - this is generally considered suboptimal for bone health and has been associated with increased risk of diabetes, inflammatory diseases, cardiovascular disease and cancer. Although a “normal” level of vitamin D is >30 ng/mL, most functional practitioners agree that it is still too low for optimal health.

Low vitamin D has been closely linked to autoimmune and chronic inflammatory disease, however some authorities believe that low 25(OH)D is a consequence of chronic inflammation rather than the cause. Low vitamin D levels during pregnancy have also been associated with higher rates of postpartum depression.

Symptoms of deficiency may include fatigues, insomnia, bone pain, hair loss, depression, muscle weakness, loss of appetite, frequent illness, and/or new onset of inflammatory condition. In some cases, a very low Vitamin D level can result in hospitalization!

How to Get Vitamin D: Sunshine and Supplements

Unlike most vitamins, food sources of Vitamin D are very limited. Only about 10 percent of the vitamin D the body needs come from food, and the rest the body makes for itself. The few foods that contain vitamin D are fatty fish (like tuna, mackerel, salmon), Liver, Egg yolk, mushrooms grown under UV light, and fortified foods (milk, cereal, orange juice). Because these foods are not often consumed in great quantities, it’s important to look at other sources of Vitamin D: sunshine and supplementation.

The best source of Vitamin D is the sun, however the amount produced depends on the skin pigmentation, the latitude, clothing, sunscreen, season, the time of day, and gut/kidney/liver health. For most North Americans, the UVB rays are not strong enough October - April. Latitudes that are further away from the equator tend to reduce synthesis rates due to less exposure to solar radiation. So for most of us, Vitamin D is best synthesized and stored in the summer months.

Image courtesy of Grassroots Health

Research has found that there are some limitations as to how much vitamin D the body produces. One study found that the amount of serum 25(OH)D produced was determined by the amount of cholesterol in the skin. As the skin ages, there is a decline in the cutaneous levels of 7-dehydrocholesterol, resulting in a marked reduction of the skin’s capacity to produce vitamin D3.

Another consideration is the amount of melanin in the skin. Darker skin types may require up to 6 times the exposure a white person does to produce the same adequate amounts of vitamin D. For example, it is estimated that takes about 15 minutes in the sun for a person with lighter skin to generate enough vitamin D for the day, whereas a person with darker skin needs anywhere from 30 minutes to three hours.

Gut health is also a limiting factor when it comes to maintaining healthy vitamin D levels. Celiac disease, chronic pancreatitis, Crohn's disease, Colitis, leaky gut, and cystic fibrosis all affect the amount of stomach acid, pancreatic secretions, bile from the liver that are available for digestion and can reduce vitamin D absorption.

Other health conditions that may inhibit vitamin D production are certain types of liver disease that prevent processes essential to vitamin D metabolism from occurring. Likewise, levels of the vitamin D can be a reflection of the health of the kidneys, so in someone with kidney disease, bioactive vitamin D levels decrease as the disease gets worse, and in end-stage kidney disease, the level is undetectable.

Vitamin D deficiency is very common: approximately 41% of men and 53% of women in the United States have levels of 25(OH)D below 28 ng/ml (70 nmol/L) - this is generally considered suboptimal for bone health and has been associated with increased risk of diabetes, inflammatory diseases, cardiovascular disease and cancer.

On a sunny spring or summer day, just 10 to 15 minutes of sunlight or exposure to a small area of skin (e.g. the forearm or face, etc.) every day, without sunscreen, can encourage a healthy production of vitamin D. A good rule of thumb is that if your shadow is longer than you are tall, the sun’s rays are not strong enough to produce vitamin D.

Mid-day is ideal when the sun is directly overhead and the hotter the better! According to Harvard Health, warm skin is a more efficient producer of vitamin D than cool skin.

The Best Vitamin D Supplement

During the cooler months, it’s almost necessary to supplement with vitamin D to ensure sufficiency. Most people will need 1000-4000 u/day to support healthy levels, but getting lab work done to determine your “normal” is best for determining how much you will need.

When supplementing D3, it’s important to pay attention to other co-nutrients like magnesium and K2. Magnesium and K2 work with vitamin D and calcium by helping calcium move into the bones. This is a major help in reducing inflammation, helping in mitochondrial

function, also lowers insulin resistance, helps with varicose veins, may help autoimmune conditions.

While I provide individualized nutrition therapy, optimizing Vitamin D is one of the few recommendations I make across the board because it affects everything! I recommend a D3/K2 supplement in the morning with breakfast and magnesium in the evenings (bonus: magnesium helps with sleep!). For more information on supplements I recommend, check out my Everyday Wellness protocol!



Clemens, TL, JS Adams, SL Henderson, and MF Holick. “Increased skin pigment reduces the capacity of skin to synthesise vitamin D3.” The Lancet, 1982.

9 Things that Can Undermine Your Vitamin D Level. Harvard Health.

For health professionals: position statement on supplementation, blood levels and sun exposure Vitamin D Council. Vitamin D Council. Jan 12, 2010. Available at

supplementation-blood-levels-and-sun-exposure/. Accessed 28 Apr 2013.

Mangin M, Sinha R, Fincher K. Inflammation and vitamin D: the infection connection. Inflamm. Res. (2014) 63:803–819

Maurya VK, Aggarwal M. Factors influencing the absorption of vitamin D in GIT: an overview. J Food Sci Technol. 2017 Nov;54(12):3753-3765. doi: 10.1007/s13197-017-2840-0. Epub 2017 Sep 23. PMID: 29085118; PMCID: PMC5643801.

Melamed ML, Michos ED, Post W, Astor B. 25-hydroxyvitamin D levels and the risk of mortality in the general population. Arch Intern Med. 2008 Aug 11;168(15):1629-37. doi: 10.1001/archinte.168.15.1629. PMID: 18695076; PMCID: PMC2677029.

Williams , J ennifer Anne, et al. "Vitamin D levels and perinatal depressive symptoms in women at risk : a secondary analysis of the mothers, omega-3, and mental health study." BMC Pregnancy and Childbirth 16.1 (2016): 203.

Yong Zhang, Donald Y. M. Leung, Brittany N. Ric hers, Yus en Liu, Linda K. Remigio, David W. Riches, And Elena Golev a. Vitamin D Inhibits Monocyte/Macrophage Proinflammatory Cytokine Production by Targeting MAPK Phosphatase-1. The Journal of Immunology, Marc h 1, 2012

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