It is not necessary to take vitamin D every day. If you need to take vitamin D because your blood levels are low, you can take it every few days, weekly, or even monthly, because, as you mention, it is fat-soluble and, therefore, stored for future use within the fat in your body. It really depends on how you’ll best remember to take it. Just adjust the dose so that you get the same total amount over time, such as 1,000 IU daily or 7,000 IU weekly.
Keep in mind that taking too much vitamin D at one time can have negative effects. For example, while it has been proven that taking vitamin D can reduce falls and fractures in the elderly, a study which gave a single annual dose of 500,000 IU actually increased falls and fractures, particularly in the first three months after being taken. Excessive vitamin D can cause hypercalcemia (too much calcium in the blood, with symptoms including constipation and weakness).
More details about dosage, uses, how to increase absorption of vitamin D, and ConsumerLab.com’s latest tests and comparisons of vitamin D supplements are found in the Vitamin D Supplements Review >>