Do I need to supplement Vitamin D if I drink fortified milk?

    It depends...

    Possibly.

    The Recommended Dietary Allowance (RDA) for Vitamin D is currently set at 600–800 IU/day (15–20 mcg) for adults. Fortified milk typically provides 100 IU per 8 oz serving (236 mL).[1] So while milk can provide a good amount of vitamin D it may not be sufficient to ensure adequate daily intakes.

    In fact, adults who rely on food sources alone for vitamin D may only be getting half their daily vitamin D requirement on average.[2][3] Those who take a vitamin D supplement are much more likely to achieve the RDA.[2][3][4]

    Doses higher than the RDA may be warranted in cases of deficiency, non-response at lower dosages, or in those with a BMI >30.[5][6][7] In these cases, a 1,000–2,000 IU/day (25–50 mcg) dose (or greater) of vitamin D may be necessary.[5][6][7]

    So, unless you are drinking 6+ glasses of milk a day, consuming other vitamin D rich foods (fatty fish, egg yolks) or considering supplementation will be required.

    References

    1. ^Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, A Catharine Ross, Christine L Taylor, Ann L Yaktine, Heather B Del ValleDietary Reference Intakes for Calcium and Vitamin D
    2. ^Fulgoni VL 3rd, Keast DR, Bailey RL, Dwyer JFoods, fortificants, and supplements: Where do Americans get their nutrients?J Nutr.(2011 Oct)
    3. ^Blumberg JB, Frei B, Fulgoni VL, Weaver CM, Zeisel SHContribution of Dietary Supplements to Nutritional Adequacy in Various Adult Age GroupsNutrients.(2017 Dec 6)
    4. ^Moore CE, Radcliffe JD, Liu YVitamin D intakes of adults differ by income, gender and race/ethnicity in the U.S.A., 2007 to 2010Public Health Nutr.(2014 Apr)
    5. ^Zittermann A, Ernst JB, Gummert JF, Börgermann JVitamin D supplementation, body weight and human serum 25-hydroxyvitamin D response: a systematic reviewEur J Nutr.(2014)
    6. ^Kennel KA, Drake MT, Hurley DLVitamin D deficiency in adults: when to test and how to treatMayo Clin Proc.(2010 Aug)
    7. ^Bordelon P, Ghetu MV, Langan RCRecognition and management of vitamin D deficiencyAm Fam Physician.(2009 Oct 15)