In fairness I did say I was referring to those in good general health. I fully appreciate there are individuals who's uptake may be impaired. Myself I suffer from a chronic bowel disorder, and I have spent many years living in poverty, so I fully appreciate how life circumstances can influence ones diet. What I will say though, is that it really is a myth that eating healthy is more expensive, because when it comes to shopping its meat, dairy, alcohol, coffee and processed foods that are expensive, take these out of the equation and most people should be able to put together a balanced diet on even the most modest of budgets.
Here's a bit of info as to why I mentioned magnesium.. "the amount of magnesium your body actually uses is different than the total amount of magnesium found in a food or supplement – in fact researchers have found that the average magnesium absorption by the digestive system is only 20 to 50%. Those who are particularly vulnerable to magnesium deficiency may need to take extra steps due to the inability of their bodies to assimilate magnesium properly. They include: Those above the age of 55Those who regularly consume alcohol, caffeinated beverages or sodasThose taking certain medications such as diuretics, heart and asthma medications, birth control pills and/or estrogen replacement therapyThose undergoing significant psychological or physical stress, including surgery, burns and liver diseaseThose suffering from digestive disorders" This isn't even talking into account people who simply can't afford enough of the types of food which provide a healthy diet every day.
I understand what you are saying about the nutrient contents of foods often being less than in the past, but a balanced diet should easily cover rda's for those in good general health. Magnesium is in loads of foods, such as ; leafy greens, many wholegrains ( like wheat, oats, quinoa), seeds & nuts, bananas, legumes ( like lentils, chickpeas, peas and many beans), avocado's, dark chocolate, tofu, fortified cereals, bread, potato's, and fish, yoghurt and milk for those who eat animal products.......the list is plentiful and I could add more. The problem is so many people eat what they want and not what they need and then try and plug the gaps with supplements and digestive aids.
Actually there are a few minerals that are quite hard to get enough of, magnesium for instance. food today is far less nutritious than it used to be due to over farming and fertilisers.
If you eat a balanced diet and are in good general health, you don't need to take multivitamins.