Hello comrades and welcome to the second improvement megathread of December! 
I hope your December is going great so far! How was your week? Any plans for next week?
Poster caption: "300 Years Since Reunification of Ukraine with Russia. Our Strength is in Brotherly Friendship!"
Good luck with your goals! 
Yeah if you're not getting at least 15 minutes of sunlight on your skin daily, you should take supplements. You can buy them in a pharmacy or order online.
IU means international units, that's the measuring unit for vit D. You can buy it in pills or a dropper form. So for example if one pill contains 1000 IU of vit D, you can take 2 pills per day.
It's safe to consume, I take 5000 IU every day during winter. I also take a magnesium supplement in order to increase absorption of vit D. I did a blood test a few years ago and found that I'm deficient in vit D. It's one of the most common deficiencies in the world. I've managed to get to normal levels by sunbathing and supplementing.
Been on this combo for the past two/three weeks and it definitely helps.