[Fraser Russell]

Fraser Russell asked the Naked Scientists:
   
Does body size affect vitamin requirement? For example, if I am an 8 stone adult and you are a 16 stone adult, but not obese, do you need twice as much Vitamin D as I do?

What do you think?

[chris]

This is a tricky one; in general, fat soluble vitamins are likely to be less of a problem than water soluble ones. The body can store fat-soluble vitamins like Vitamin A, D, E and K within adipose tissue and in fat deposits in organs (like the liver). Most people therefore have a reasonable long term store of these agents and therefore are unlikely to ever "run out" on the grounds of large stature.

With water-soluble vitamins - such as the B vitamins - people are more prone to deficiency states because these agents are very hard to retain in the body for any period of time. Any excesses are usually flushed away in urine.

I think, as a rule of thumb, a big person - e.g. with a large bulk of lean tissue and running a significant metabolic rate - will have a higher demand for vitamins than a smaller person, and the demand for water-soluble vitamins is likely to be higher at times (owing to an inability to store these agents) than for fat-soluble ones. That said, the relatively tiny amounts of both that are actually needed to keep a person healthy mean that most people, large or small, are vitamin replete for the majority of the time.

A slightly "woolly" answer, for which I apologise. Perhaps someone else can do better?

Chris

[CliffordK]

Good Point.

Fat doesn't necessarily mean it needs more nutrients of any kind.

Children and Teenagers may need more nutrients than an adult.

[Kevan Gelling]

A paper published in European Journal of Endocrinology describes a formula that can be used calculate the amount of vitamin D needed in a single dose to correct a person's vitamin D levels [?].

The cholecalciferol loading dose required to reach the serum 25-OHD3 target level of 75 nmol/L can be calculated as follows:

Dose (IU) = 40 x (75 - serum 25-OHD3) x Body Weight

The researchers found that body weight was directly linked to the amount of vitamin D required.

Two caveats:
- The calculation is for a 'correction' dose, not a maintenance dose.
- The formula does not include BMI (i.e. obesity) which is known to affect the efficacy of vitamin D and may be more significant that body weight per se

van Groningen, L. et al.  Cholecalciferol loading dose guideline for vitamin D deficient adults. European journal of endocrinology / European Federation of Endocrine Societies (2010)