Vitamin D3 (and the K2 that goes with it)

What it is

Vitamin D contributes, under authorised claims, to normal absorption and use of calcium and phosphorus, to the maintenance of normal bones, teeth and muscles, and to normal immune system function. In a supplement the dose must be checked: the EFSA tolerable upper level for adults is 100 µg (4,000 IU) a day.

Also, high spaced doses (ampoules, monthly regimens) are medicines decided by the doctor. At the counter we only discuss the daily supplement dose.

What it does

It helps absorb calcium in the gut and keep it in bone:

• Sunlight makes it in the skin, but in winter and in older people it falls short.
• K2 is added to many products for calcium, with no authorised claim of its own for that pairing.
• The level is measured with a blood test, not guessed.

At the counter

When to recommend it

• Daily dose within the tolerable upper level, with the fattiest meal of the day
• When a blood test or their doctor indicates a shortfall
• The time of day does not change the effect

When not to

• High doses without medical supervision (4,000 IU a day kept up or more)
• Hypercalcaemia or calcium kidney stones without checking first
• Combined with K2 in anyone on acenocoumarol or warfarin, without warning

Warnings

• Important VITAMIN K ANTAGONIST ANTICOAGULANTS (acenocoumarol, warfarin): vitamin K2 can reduce their effect. Do not offer D3+K2 without telling their doctor.
• Important EXCESS: high doses kept up cause hypercalcaemia (nausea, thirst, stones, arrhythmias). More is not better.
• Caution Thiazides and added calcium raise the risk of hypercalcaemia; sarcoidosis and some kidney diseases too.
• Worth knowing Very high dose preparations are medicines with a medical indication.