If I understand what my Chiropractioner said and from what I've read in 'bone-ology' text books correctly, then your bones, especially back bones - because they were never particularily designed for bending & lifting heavy objects, evenutally start to disintegrate, due to degredation of the bone and damage to associated ligaments and discs. Now all this is relative. So if you started doing heavy manual work at a youngish age AND, spent all your time lifting using correct methods etc., you should end up with less problems (because your muscles, ligaments, discs etc. have developed bulk & strength), than someone who starts off at a later age when the body cannot develop muscle bulk, ligament strength etc., to the same degree as a younger person. This is partially why footballers deliberately develop muscles which are larger than they actually need for the game of football. It gives their joints a degree of protection from damage.
Taking supplements may help. But... the body can only absorb and use a fixed amount of calcium (or other minerals). All the excess which cannot be taken into use either gets absorbed elsewhere in the body as calcium deposits or is excreted. This varies from person to person and their age. Which is why kids were once given free milk at school because they were able to use up the calcium. As an adult your body needs less and cannot absorb any more. So taking extra calcium is unlikely to work(unless you are not taking enough already) and can cause probems with calcium deposits in unwanted parts of the body if you take too much.
I absolutely agree with you regarding strengthening the arms, shoulders and other upper body muscles. My partner of ovef 20 years says that she can see the difference now than when I worked in an office then.
I'm not complaining though about my back - it only causes odd problems, I get more satisfaction now from building a nice wall or laying a hedge (or any of the other things I now do) than I can recall ever getting from dealing with corporate crap.
