Quick answer Feeling tired is not enough to conclude you need iron. Low iron is common, especially in people who menstruate, in pregnancy, and in some vegetarians and vegans, and it can cause fatigue, pale skin, shortness of breath, and brittle nails. The way to know is a blood test: a serum ferritin below 30…

Quick answer Most healthy adults do not need to take probiotics daily. Probiotics have the strongest evidence for specific situations, such as reducing diarrhea linked to antibiotics and helping some gut conditions, and they may help prevent traveler’s diarrhea. For general wellness in healthy people, the evidence is weak and inconsistent, and many commercial products…

Quick answer Yes, you can take too much vitamin D, but it is uncommon at normal doses. For most adults the tolerable upper intake level is 4,000 IU (100 micrograms) per day unless a doctor prescribes more. Vitamin D raises calcium absorption, so the main danger of excess is high blood calcium, which can cause…

Quick answer Collagen supplements show small, real-looking improvements in skin hydration and elasticity in some short trials, but the evidence is weaker than the marketing suggests. Many studies are small, short, and funded by the companies selling the products, and a 2025 review concluded there is not enough clinical evidence to say collagen prevents or…

Quick answer Magnesium is involved in the body’s sleep-regulating systems, and people who get more of it tend to report better sleep in observational studies. When magnesium has been tested as a supplement in randomized trials, the results have been mixed: some small trials found modest improvements in sleep quality or how long it took…

Quick answer The baseline recommendation is 0.8 grams of protein per kilogram of body weight per day, which for a 68 kg (150 lb) adult is about 55 grams. Most adults already hit this from food, but older adults and very active people often benefit from more, roughly 1.0 to 1.2 grams per kilogram for…

Quick answer Gummy vitamins are convenient and easier to take, but they are usually not “as good” as pills or capsules in a few specific ways. Gummies tend to have added sugar, often contain fewer nutrients per serving, can deliver less consistent doses, and degrade faster over time, and many contain no iron. For most…

Quick answer The simple rule is to take most vitamins with food. The fat-soluble vitamins (A, D, E, and K) are absorbed much better with a meal that contains some fat, and taking any vitamin with food reduces the chance of an upset stomach. Water-soluble vitamins (the B vitamins and vitamin C) can be taken…

Quick answer For many people, yes, winter is when vitamin D status drops the most, because skin cannot make vitamin D from weak winter sunlight. This matters most above roughly 35 to 37 degrees latitude, where winter sun is too weak for months at a time. Adults need about 600 IU (15 micrograms) a day,…

Quick answer For most healthy adults who eat a varied diet, a multivitamin is not necessary, and large studies show it provides little or no benefit for preventing heart disease, cancer, or early death. A multivitamin is not a substitute for food, and there is no standard definition of what one must contain. They do…