Very good advice Red_Star. Magnesium deficiency is very common.
Excerpt from the article: Know the Importance of Taking Enough Magnesium with Your Vitamin D...
"Vitamin D, just like all other nutrients, works in harmony with several other nutrients to perform its many functions. Most importantly, vitamin D requires and 'uses up' magnesium to convert from supplements or sun into its active form in the blood. As such, it is a big mistake to simply take large doses of Vitamin D without taking the need for magnesium into consideration. Yet this is exactly what is happening in most cases and it is causing a lot of people to have problems that they believe are due to side effects of Vitamin D- or even worse they believe they are experiencing an overdose.
Such a huge number of people have subtle magnesium deficiency that some researchers and doctors are calling magnesium deficiency an epidemic, and anyone with even a mild or 'subclinical' magnesium deficiency will have this deficiency amplified when Vitamin D is taken. This is creating some uncomfortable 'Side Effects of Vitamin D' that are actually symptoms of an induced magnesium deficiency! Some of the magnesium deficiency symptoms being attributed to Vitamin D are:
Spasms such as these are often caused by a deficiency of calcium, magnesium, or potasium. For two hundred years quinine sulfate was available over the counter until the FDA banned it about six years ago. I have some and it is very helpful. Drinking water is not relevant. Try drinking a glass of milk, eating a banana and getting a supplement of magnesium gluconate.