Not actually true Gmamilly that a well balanced diet always does the job.
As we age, our ability to absorb everything we need from our food declines. Also we don't get enough Vit D from our diet but rely on sunshine to top it up. It is well documented and researched that Brits ought to take a Vit D supplement in the dark, winter months.
Also, as many of our animals are not grass-fed any more, and many of our grasslands are over farmed and mineral depleted, we cannot assume that our diet does contain everything we need these days.