Cofactors need to be adjusted when taking a lot of vitamin D for more than a month
"A lot" is more than 4,000 IU Vitamin D daily (average)
There is virtually no agreement as how much of each cofactor is needed vs vitamin D level
The first three cofactors have, like vitamin D, greatly decreased in the human diet in the past 50 years
The goal is to restore Vitamin D, Magnesium, Omega-3, and Vitamin K back to where they had been
   in a nutshell = summed up = condensed

Magnesium

• Only about 1 in 300 people seem to be allergic to Vitamin D
     but the allergic reaction is often due to lack of Magnesium
• Magnesium increases the benefits of vitamin D by about 30% (Mg and Vit. D are synergistic)
• Magnesium provides a great many health benefits independent of Vitamin D
• 100 milligrams of Magnesium (say from Magnesium Chloride) seems to be enough, even with high levels of vitamin D
      see Overview Magnesium   Magnesium category has 197 items

Omega-3

• Omega-3 increases active vitamin D - especially in people with poorly functioning livers or kidneys
• 1 gram of Omega-3 seems to be enough. Note: different brands have widely different bio-availability
  I prefer Vetomega brand
• - see Overview Omega-3  Omega-3 category has 207 items

Vitamin K2

• K2 Keeps Calcium in bones and out of arteries
• Calcification due to K2 deficiency may be a reason for increased mortality for some diseases for high vitamin D
• Perhaps 100 micrograms per 2,000 IU of vitamin D (i.e. 500 micrograms for 10,000 IU of Vit D)
• Perhaps should not take K2 concurrently with Vitamin D. Vitamin D decreases the uptake of Vitamin K1 by 50%
• - see Overview Vitamin K2   Vitamin K category has 89 items

Calcium

• Too much Calcium is associated with cardiovascular problems years later, not stronger bones
• Should have less than 750 milligrams of Calcium supplementation
• Drinking a lot of water helps flush any excess Calcium from the Kidneys
• - see Overview Calcium   Calcium category has 170 items

Boron - good, but not as essential

• Boron increases Vitamin D and Magnesium in the body by ~ 20%
• Most people Boron deficient now that commercial fertilizers are used
• Should have 3-10 milligrams of Boron element daily
• Boron can be extremely low cost, less than $0.01 a day
• - see Boron category has 20 items

Unfortunately

• The cost of cofactors is 10X to 100X more than the vitamin D
• Many of the cofactors must be taken daily (vs bi-weekly for Vitamin D)

See also VitaminDWiki

• Too much Vitamin D long-term problems if take too much vitamin D without balancing cofactors
• Low cost cofactors for vitamin D - includes listing of what the founder of VitaminDWiki actually takes
• Supplements category listing has 76 items along with related searches
• Vitamin D Receptor is one of the genes which can block vitamin D from getting to the cells
     The standard Vitamin D test cannot detect a poor Vitamin D Receptor
     Adding more Vit D, Mg, Omega-3, Boron?, Resveratrol, etc increase Vit D to the cells

See also web
Excellent information on virtually all supplements as well as Vitamin D

• ConsumerLabs $42/year - has a 5 day free trial. lower cost for 2 year subscription
• Examine.com