No one argues that we need Vitamin D. Although we call it a vitamin, our bodies also produce Vitamin D, along with melatonin, when we expose our skin to sunlight. According to Patrick Quillin PhD, RD, CNS, in his book Beating Cancer with Nutrition, both Vitamin D and melatonin help “squelch” cancer and enhance the immune system. Vitamin D also maximizes the good effects of eating greens by decreasing blood pressure, improving arterial function, and activating chlorophyll by-products in our blood to make Co-Q 10 — a naturally occurring enzyme in the body that works as an antioxidant. Vitamin D promotes bone health as well, and can be found in egg yolks, fatty fish, and chicken liver. https://healthyeating.sfgate.com/raise-vitamin-d3-level-3561.html
I like to check Dr. Greger’s short videos on various topics because he compiles and condenses research to get to the gist of various studies. (https://nutritionfacts.org/2019/05/02/the-best-source-of-vitamin-d/)
So Vitamin D is good stuff, and we who shiver under dark skies four months of the year may not get enough. The dilemma lies in how we choose to access it. One answer is to go outside and soak it up. Yet the Academy of Dermatology urges that we avoid any exposure to sunlight unless we wear sunscreen to protect us from cancer. (https://nutritionfacts.org/2019/05/07/is-the-risk-of-skin-cancer-from-sun-exposure-overblown/).
However, Dr. Mercola, a popular functional medicine practitioner, has some concerns about sunscreen. (https://articles.mercola.com/sites/articles/archive/2019/05/22/oxybenzone-sunscreen-health-risks.aspx). And if you’re not confused enough, I disagree with Dr. Mercola about titanium dioxide being safe. More than one site I read cited it as a possible carcinogen.
Is Supplementation the Solution?
It seems that taking Vitamin D3 supplements can boost blood levels. Yet, I was disheartened to learn that not all purported doses were correct, and often the actual dose was lower than that on the label. Worse yet, several labs found different blood levels of Vitamin D in the same sample.
We need it. We risk cancer and skin damage getting Vitamin D without sunscreen that block the rays that bring it to us and harbor harmful chemicals to boot. Supplements work but how do you know you received the right amount. Is your blood level too high or low? Was the lab result accurate? Do you need more Vitamin D or less?
Fat-soluble vs. Water-soluble Vitamins
And just in case you overdid the supplement thing, signs of Vitamin D toxicity include too much calcium in the blood and urine, loss of appetite, nausea/vomiting, needing to urinate frequently, muscle weakness, joint pains and disorientation. Unlike water-soluble vitamins, Vitamins A,D,E,and K are fat soluble vitamins. We excrete excess water-soluble vitamins in our urine, but fat-soluble vitamins can build up in our fatty tissue and cause side effects.
I can tell you my integrative physician said my level should be 40, while my “regular” doctor is happy at 20. Toxicity could begin with blood levels greater than 150. This site explains matters in greater detail (https://www.healthline.com/nutrition/how-much-vitamin-d-is-too-much).
Now that you know the facts, you can determine how you will achieve the protective level of Vitamin D3 your body needs. I suspect moderation in all approaches is the safest bet until further research provides more guidance.
 Beating Cancer with Nutrition, Patrick Quillin, Nutrition Times Press, Inc. p.279