So you're taking Vitamin D. Well done, you! This means you've already begun taking preventative steps to protect yourself against joining the other 40% of the U.S. Population that is D-ficient. This is huge given the role Vitamin D plays in bone health and immunity.The question now is - how much should you take?Having already learned that Vitamin D might be better absorbed with food and that Vitamin D3 is better than D2, let's now explore the dirty details on how much D you should down.How much Vitamin D do I need?Well, it depends. Age, body weight, and race are all important determiners, as are environmental factors such as latitude, season, and sun exposure.Overweight individuals likely require higher amounts of Vitamin D. One study found that obese persons should increase their supplementation by two or three times the amount recommended for their age group.Similarly, due to greater levels of melanin in the skin, people with darker skin tones need more time in the sun to produce the same amount of Vitamin D as their fair-skinned peers. This would suggest that those with darker skin tones should supplement at slightly higher doses because their bodies are even less likely to be able to produce adequate Vitamin D from the sun alone.Recommendations based on ageMost commonly, Vitamin D dosage is based on age. And, although not everyone agrees 100% (but when do we ever), here are the general guidelines.Per the Institute of Medicine: Infants age 0 to 6 months: adequate intake, 400 IU/day; maximum safe upper level of intake, 1,000 IU/dayInfants age 6 to 12 months: adequate intake, 400 IU/day; maximum safe upper level of intake, 1,500 IU/dayAge 1-3 years: adequate intake, 600 IU/day; maximum safe upper level of intake, 2,500 IU/dayAge 4-8 years: adequate intake, 600 IU/day; maximum safe upper level of intake, 3,000 IU/dayAge 9-70: adequate intake, 600 IU/day; maximum safe upper level of intake, 4,000 IU/dayAge 71+ years: adequate intake, 800 IU/day; maximum safe upper level of intake, 4,000 IU/dayPer Vitamin D expert Michael Holick, however, both infants and adults should be taking 1000 IU a day.One study even found that, for people with a Vitamin D deficiency, 5000 IU was needed to bring their Vitamin D blood levels back within normal range.The Vitamin D Council, a non-profit based in California, also suggest 5000 IU a day for "the average adult". Why? A study featuring traditionally living people in East Africa (i.e. hunter gatherers, just like our ancestors) found their average Vitamin D levels to be 46 ng/ml. Following the assumption that this was the geographic region in which humans evolved and, therefore, that humans also evolved to need around 40-50 ng/ml of Vitamin D, 5000IU was stated as a good general estimate. According to this study, 5000IU a day is needed for the average adult to reach 40 ng/ml a day - this, of course, still depends on age, weight, and routine sun exposure.Okay but I want a straight answerYou should at least take 600 IU a day. But, given that many (wait, all) of us don't spend the majority of our time outdoors in minimal clothing the way our ancestors did, you likely need closer to 2000 IU a day.And if you've had blood tests that prove you're deficient? Go higher. Yes, Vitamin D can be toxic when overdone, but you'd need to take upward of 4000 IU (at least) to even come close to risking it. Plus, as we've just seen, some sources actually recommend starting at 5000 IU a day.Ultimately, it's your call. If you're particularly concerned about being Vitamin D deficient, or if osteoporosis runs in your family, a blood test detailing your Vitamin D levels might help you decide. As might checking with your doctor or nutritionist (it's easy, just give 'em a call).Have any questions? Give us a holler.