If you feel groggy halfway through the day, don’t guzzle more coffee.
Pop vitamin D instead. According to the Journal of Clinical Sleep Medicine, low levels of “D” are linked to daytime sleepiness. Here’s why: Vitamin D helps keep bones and muscles healthy – so too little can cause weak muscles, and sore joints that could keep you up at night. Also, low vitamin D levels are linked to inflammation – which directly causes sleepiness. So start popping up to a‑thousand International Units of vitamin D daily. Especially if you suffer from milk allergies, or are a vegetarian or vegan, and are getting less “D” than average.