Since the Food and Drug Administration does not currently regulate supplements, few studies exist on which vitamin brands specifically have the best absorption rate. Instead, there are many claims by each company as to the quality and absorption of their product. It is also hard to say which brands have the best absorption, as this usually depends on the individual as much as the product. Several ways to determine which vitamins will be best absorbed include if they are enteric-coated or not, your own digestive capabilities as you age, and if the vitamins include nutrients that balance each other.
Work with a health care provider who understands supplementation, nutrient deficiencies and absorption issues to find the best supplement for your body.
Certain nutrients, such as those found in omega-3 fatty acids and probiotics, need protection from stomach acids so that they can make their way into the small intestine. For these types of nutrients, enteric-coating is necessary to protect the sensitive oils, bacteria or nutrients from degradation, according to "Smart Medicine for Healthier Living" authors Janet Zand, Allan N. Spreen and James B. LaValle. Otherwise, the usefulness of the nutrient is limited.
One important thing to consider when taking a vitamin supplement is your own digestive capabilities. Supplements are better absorbed when taken with food, as the digestive enzymes and hydrochloric acid excreted help break them down. Age is also a factor in digestion, as it tends to become less efficient over the years, according to the book "The Complete Idiot's Guide to Glycemic Index Weight Loss" by Lucy Beale and Joan Clark. This means less nutrients are absorbed from both foods and vitamins, so adding digestive enzymes may be necessary.
Work with a qualified nutritionist or practitioner to determine the best ways to increase absorption as you age.
The absorption of some vitamins is actually based on and improved by other nutrients. Calcium absorption, for instance, is increased by the presence of vitamin D, which, according to "Understanding Normal and Clinical Nutrition," helps to make the calcium-binding protein needed for absorption. Zinc and vitamin C are known to decrease the absorption and retention of copper in the body. A high intake of calcium may decrease magnesium absorption, according to the book "DRI, Dietary Reference Intakes: The Essential Guide to Nutrient Requirements." In other words, it is important to find a multivitamin that contains nutrients that balance each other for proper absorption. If taking a single vitamin, find out if another vitamin is necessary for increased absorption or to prevent deficiency.