Several years ago, I started looking into why I was feeling so crappy. I stopped eating candy/sugar, ramped up a healthier diet. Eliminated all other culprits. But still.. Always tired. . Frequent sniffles. - - One of the issues I stumbled across was VIT D3 deficiency. So I had my D3 tested. Yes! I tested BELOW 20 ng/mL Which means DEFICIENT. (There are reputable Labs online, selling finger prick kits. ~$50 - $60 if you don't have insurance. No doctor/lab visit. All done through the mail). - - Why deficient? I sit in a DARK office all day., using software to draft engineering plans. Most everything I like to do is INDOORS in rooms with NO windows, ie. dance studios, music rehearsals.. - - I take 10,000 IU D3/day with 200mg VIT K2 (as Mk7). VERY important to consume with K2 to avoid Kidney stones and properly absorb the D3. - - I have read that 10,000 IU/day is dangerous. I call BULL. Blood levels Under 20 ng/mL = Deficient. Over 99 ng/mL = Too High. My yearly D3 blood level hovers between 49 and 55 ng/m.. I could actually take MORE! But I am leery of developing Kidney stones. I've been taking Healthy Origins Vitamin D3 10,000 IU for several years, with decent test results. NOT toxic. - - I can't say I am leaping out of bed every morning but fact is, I stopped getting sick. NO colds, flu, low grade fevers. No ANYTHING. I started taking 10,000 IU D3/day TEN years ago. Since then? Not one sniffle or sore throat. This can't be a coincidence.