How much vitamin D is too much?

DEAR DR. ROACH: I recently had a blood and urine checkup. Most everything was within normal range (doing well), except that I am low on vitamin D, at 24. The doctor recommended supplements, but said to be careful not to overdo. How much is too much? Is one a week OK?

ANSWER: There are several ways to replace vitamin D, but the most common are weekly ergocalciferol (vitamin D-2, usually given as 50,000 units for eight weeks) or cholecalciferol (vitamin D-3, taken daily).

I prefer daily vitamin D-3 as a supplement for most people who are found to have low vitamin D levels.

Most people remember better to take one daily, and many people think that after a month of taking weekly vitamin D they are cured and do not take the required follow-up supplements.

While it is true that excess vitamin D can be dangerous, it is very uncommon to have excess vitamin D when taking 8,000 units or less daily. (Some people will need more than that, but doses in excess of 8,000 IU should be guided by blood levels. Some people don’t absorb vitamin D well, and they may need amounts that might cause toxicity in other people.)

The general recommendation is 1,000 to 2,000 units of vitamin D-3 daily. However, D-2 comes in 5,000 and 10,000 units in addition to the 50,000, so it is fine to use weekly dosing if you prefer.

DEAR DR. ROACH: About four months ago I was in the emergency room with pain in my lower back. The doctors did a CT scan, which found an 8 mm kidney stone requiring a procedure to break up the stone, as it would not pass.

The kidney stone was calcium oxalate monohydrate. What causes this? It was extremely painful, and I do not want another. The doctor emphasized drinking lots of water with lemon.

ANSWER: There are several possible reasons why people form calcium oxalate stones, but in any given person it may be impossible to identify the one particular cause.

Family history, diet, medications, water intake and anatomical issues all might predispose a person to developing a kidney stone.

Calcium and oxalate both are important, but the calcium story is slightly confusing. As you might expect, taking calcium supplements increases risk of developing calcium stones, because the calcium, often taken without food, is excreted by the kidney and increases stone formation.

However, calcium in food has the opposite effect: High-calcium diets are associated with a decreased risk of forming stones. This is thought to be due to the fact that calcium in food binds oxalate in foods, and the decreased oxalate means fewer stones. Oxalate, however, is found in many foods.

A registered dietician nutritionist can help you, but I recommend this page from my former professor Dr. Fred Coe and his team: tinyurl.com/h2loheu.

Other dietary factors that will reduce the risk of another calcium oxalate stone are: reducing animal protein and increasing (most — check the list) fruits and vegetables; decreasing sodium intake; and reducing sugars (specifically sucrose and fructose, apart from what is found naturally in fruits).

Citric acid, in the lemon your doctor recommended, helps to prevent stones in some people. It also may be taken as a pill, as potassium citrate.

The other piece of advice your doctor gave you might be the most important of all: Drink plenty of water. People who are prone to kidney stones should drink lots and lots of water (coffee and tea are fine, too, despite the small amount of oxalate in tea).

Readers may email questions to ToYourGoodHealth@med.cornell.edu.