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Vitamin D3 (as opposed to D2) is recommended most often because it is the naturally occurring version of vitamin D in your body. D2 is poorly absorbed. Other possible names for vitamin D supplements include: Alfacalcidol, Calcifediol, Calcipotriene, Calcipotriol, Calcitriol, Colecalciferol, Dihydrotachysterol, and Paricalcitol. Vitamin D is a fat-soluble nutrient, which means that you need to have eaten a little bit of fat in order for the nutrient to be absorbed efficiently by your body. Fat-soluble nutrients (the other ones are A, E and K) take a long time to be absorbed and eliminated by your body because they are stored in your fatty tissues and liver.  Always take your vitamin D supplements with or right after you have eaten a meal. The food in your system will help your body to process this nutrient. It doesn’t seem to matter what meal you take your supplement with. The time of day does not appear to affect your body’s ability to absorb vitamin D. Certain medications interact with the absorption of vitamin D supplements and prevent healthy absorption. These medications include: Antacids, Lipitor, Dovonex, Lanoxin, Cardizem, Dilacor, Tiazac, Cytochrome P450 3A4 (CYP 3A4) substrates, Verapamil and water pills. Cofactors are nutrients that work together to help the body absorb as much of the nutrients as possible. For example, magnesium is known to be a co-factor of vitamin D. This means that eating foods that are rich in magnesium, or taking magnesium supplements, may help your body to absorb vitamin D more efficiently. Other nutrients that are thought to help your body absorb vitamin D include:  Boron. Foods that are rich in boron include almonds, apples, hazelnuts, dates, and avocados. Vitamin K. Foods that are rich in vitamin K include basil, kale, spinach, scallions, Brussels sprouts, and asparagus. Zinc. Foods that are rich in zinc include oysters, crab, beef chuck, fortified breakfast cereal, lobsters and baked beans. Vitamin A. Foods that are rich in vitamin A include sweet potatoes, carrots, kale, butternut squash, dried apricots, and romaine lettuce. People who are overweight tend to have low levels of vitamin D. This is because the fat cells in their body extract the vitamin D from their blood (vitamin D is fat-soluble after all) and thus vitamin D is kept from the circulation through their bodies. If you are obese, losing some weight may help you to better absorb vitamin D and increase your vitamin D levels. To lose weight:   Try to eat a healthy, balanced diet. The key to reaching a healthy weight is to make healthy choices when you eat.  Exercise regularly. In addition to eating healthy, you need to get your body moving in order to tone your muscles and burn off excess fat. As mentioned in the previous section, there are some medical conditions that can affect how your body activates vitamin D. In particular, weak kidneys can limit your body’s ability to activate the vitamin D that you consume (either through sun, food, or supplement). Talk to your doctor about options for treatment.
Choose the correct vitamin D supplement. Take your vitamin D supplement with the largest meal of the day. Examine your medications before taking vitamin D supplements. Consider increasing your intake of other nutrients that are cofactors of vitamin D. Lose some weight. Work with your doctor to try to treat underlying medical conditions that could be affecting your body’s ability to absorb vitamin D.