D is not something you can take until you get a "good reading" and then stop. The body needs it every day ..this is illustrated by how it is made in the skin from sun exposure and that replenishes what is used up in the tissues.

You started at 28, which is not really that low, compared to others here on NT. Many chronic pain patients come here and find they are below 10. The average is between 10 and 20. Then only a few hover around 30. To have a level like yours, you must be making it for yourself in the skin, and/or getting it in a fortified food or multivitamin. It has to be coming from somewhere.

Taking up to 4000IU of D3 daily is considered safe today, by the IOM.

Keep in mind that you should watch calcium intake by supplements or antacids while on high D treatment. Some cardiologists recommend no more than 600mg a day. D increases calcium absorption in the GI tract so food sources are typically much more successfully absorbed.

I think a level of 58 is pretty good. Many people here had difficulty reaching that from supplements.