As winter drew to an early close, I sat outside on a warm, sun-drenched day unable to keep from closing my eyes and tipping my head back to absorb the full warmth of the sun washing over my skin. While my leisure activity was a simple act, its impact on my body was anything but. I was working to “photometabolize” the sun to create an important hormone in my body — vitamin D. Although there are several sources of vitamin D, the most simple and effective source (and the one I preferred) was free for the taking, the sun.

Michael F. Holick, director of the Vitamin D, Skin and Bone Research Laboratory at Boston University School of Medicine, says that in order to have enough vitamin D for the year, your unprotected skin should get 10 to 30 minutes of sun, three times each week between 10 a.m. and 3 pm. Because vitamin D is fat soluble, your body will store it for extended periods of time. Andrew Weil, doctor and current director of the University of Arizona Center for Integrative Medicine, says in his article “Vitamin D, how much should I take?” that if you follow this recommendation between April and September, you will have stored enough to get you through a long Wisconsin winter.

But what about the risk of developing skin cancer from sun exposure? While sunscreens do interfere with your vitamin D absorption, not using them can significantly increase your risk of skin cancer. As with everything, it’s all about balance. So, get your 10 to 30 minutes of unprotected exposure three times each week, then cover up.

Holick cites vitamin D as the oldest known hormone, dates back at least 750 million years when phytoplankton converted the UVB penetrating the water column into vitamin D2. Holick explains in that once phytoplankton concentrated vitamin D in their bodies, the organisms made their way up the food chain, which eventually led to a diverse and rich ocean environment. Once animals moved onto the land, they developed the ability to synthesize vitamin D from the sun.

Humans did quite well until industrialization drew large populations into crowded cities where tall buildings blocked out the sun. As described by David Bishal and Ritu Nalubola in “The history of food fortification in the United States,” as far back as 1889, scientists already understood the importance of a vitamin D deficiency and doctors promoted sunbathing for healing and maintaining healthy skin.

By 1919, scientists discovered a devastating bone disease called rickets, which was connected to a malfunction in the metabolism of phosphorous and calcium due to a vitamin D deficiency among city dwellers. Harry Steenbock, professor of biochemistry at the University of Wisconsin-Madison, invented a way to fortify milk with vitamin D, and by 1932, rickets was all but eliminated.

The National Institutes of Health Office (NIH) of Dietary Supplements found in a 2010 study that 41 percent of Americans tested positive for a vitamin D3 deficiency. NIH says that Vitamin D helps protect against osteoporosis and other bone diseases. Holick points to vitamin D and its role in possibly preventing and helping treat cancer, diabetes, hypertension, glucose intolerance and multiple sclerosis. A 2014 study by researchers at the University of Oxford and the Wellcome Trust Centre for Human Genetics found links between vitamin D deficiencies and genetic and chronic diseases as well.

Joi Davis, a gynecologist/obstetrician at Oconomowoc Memorial Hospital, observes, “A lot of my patients are deficient in vitamin D3, which can go hand in hand with endometriosis, fatigue, seasonal depression, and muscle aches, but adding fortified milk to their diet improves those conditions dramatically.”

She continues, “Many of my in vitro fertilization patients also do better if (vitamin) D3 is optimized, since it is used in making a hormone produced in the ovaries that helps egg production, which means when more eggs are in the ovaries, there’s an increased chance of pregnancy.”

Getting vitamin D from the sun or unprocessed foods such as fish, pork, heavy cream, cheese and mushrooms is the least expensive way to do it. If you choose supplements, work with your doctor to assess just how low your levels are. A simple blood test will guide your doctor to recommend the proper supplement dose, time in the sun or specific foods to get your levels back on track. A complete list of foods with vitamin D can be found on the NIH website.

Recommended daily dose of vitamin D 

Children age 0 to 12 months: 400 international units 

Kids ages 1 to 18 years: 600 IU 

Adults ages 19 to 70: 600 IU 

Adults age 70 and older: 800 IU 

(Source: National Institutes of Health) 

Kathy Mydlach-Bero is the author of E.A.T. An unconventional decade in the life of a cancer patient, kathymydlachbero.com.