Vitamin D influences over 1000 genes involved in cellular growth, immune system function and genes related to autoimmune diseases, intestinal health amongst other functions. So basically your bones, your brain, your gut and everything in between are influenced by Vitamin D levels in your body. More recently, a Vitamin D deficiency has been implicated in susceptibility to Covid-19.
Referred to as the ‘sunshine vitamin’, Vitamin D is made in the skin from ultraviolet B rays from the sun. Spending 10 minutes outside on sunny days with approx 1/3 of your skin exposed (think tank top and shorts) can give most individuals the Vitamin D they need for the day. With winter around the corner, those of us in the Midwest and Northeast states cannot rely on the sun unless you work outside. Food sources of vitamin D include milk, fatty fish (swordfish, tuna, etc.), fortified cereals, swiss cheese, liver, egg yolks and beef. You would have to eat a lot of these foods to get your Vitamin D levels in the normal range. The consensus among researchers and medical professionals is people in these regions of the U.S. should supplement with a high quality D3 supplement during the winter months. If you avoid the sun year round, you should consider a daily supplement year round.
Your Vitamin D levels are determined through a blood test that measures Vitamin D 25-Hydroxy. Normal blood serum levels are 30-100. Many doctors are including this test in annual physical blood work but always ask them to include to be sure.
If you fall below normal range, your physician should suggest you take a D3 supplement. Look for a high quality supplement that has been 3rd party reviewed (e.g. ConsumerLab.com, NSF International, U.S. Pharmacopeia (USP)). A K2-D3 supplement is best for optimal uptake but get clearance for K2 since some heart disease medications require limiting Vitamin K in your diet. Take with some healthy fat for better absorption (nuts, avocado, etc.)
Starting with 600-1000 IU’s (15mcg-25 mcg) is usually the recommended. If your medical professional tells you your Vitamin D levels are too low, you would increase this to 1000-2000 IU’s per day. Some people can consume as much as 5000 IU’s per day but higher doses can lead to toxicity. Consult with your doctor if you have questions.