I have a 17 year old son who has been supplementing with Vitamin D3 without much increase in levels. He is not overweight (6 feet tall and around 150 lbs) and is not dark skinned. We live in New Mexico at the high altitude of 7,500 ft. We bought vitamin D test from the vitamin D council. He first tested April 25th with a result of 45.3. He started taking 14,000IU per day and I encouraged him to get in the sun. On July 14th, he tested again with a result of 48.2. After this test result, we switched to a VitD3/K2 supplement and increased his dosage to 20,000IU of D3 per day taken with fat (usually a spoonful of coconut cream concentrate). The K2 is 15mcg per drop and he was taking 10 drops — for the 20,000 IU of D3 and 150 mcg of K2/M7. He tested his vitamin D level a third time on October 12th with a result of 42.4. I assume that the drop in his levels are due to less sun exposure. He does not seem to be absorbing the D3 adequately from the supplement and so I hesitate to go even higher until we have explored other reasons his levels aren't increasing. I am purchasing a separate K2/M4 supplement, brand Thorne with 1mg of K2/M4 per drop. Are there any other co-factors that he might need or would aid in absorption? His only health issue is itchy feet. The severity is terrible in winter but reduces greatly in summer. The seasonal aspect is what made us think of Vitamin D, especially since many other possibilities have been eliminated (such as specific footwear, fungus, athlete's foot, food allergies, etc.). Hopefully his condition would be helped by increasing Vitamin D3 levels into the 60s and then sustaining that over the long term. Thank you for any advice you may have.