From Mayo Clinic:

"Vitamin D toxicity, also called hypervitaminosis D, is a potentially serious but treatable medical condition that occurs when you get too much vitamin D."
"....usually results from taking an excessive amount of vitamin D supplements."
Causes a buildup of calcium in your blood. Symptoms include nausea, vomiting, constipation, weakness, confusion, heart rhythm abnormalities, kidney stones.
American Academy of Pediatrics recommend children and adolescents get 400 IU daily, adults 1000-2000IU. "Supplements can be a reasonable way to meet recommended levels- as long as you pay attention to how much you take. And be sure to tell your doctor about any supplements you take.

In Canada with long dark winters and frequent cloud cover, taking vitamin D supplements is recommended.

NIH-
Factors involved in vitamin D from sunlight include season, a person's distance from the equator, skin color and clothing.

Although studies show adequate levels of vitamin D possibly lower levels of prostate cancer, and some types of cancer, exposure to too much sun causes skin cancers, according to dermatologists.
"The safest way is to take supplements" according to Dr. Sue Ingles, Univ. Southern California.