Nutrition — how much is enough?
By Dr Ross Walker
I was recently sent the below question from a man in Western Australia:
“Can you provide some information on human mineral requirements (both major and trace) as affected by age, gender and physical activities? By world standards Australian soils are generally regarded as relatively poor (proportion of clay, loam and sand) also affected by rainfall and potential for leaching. There is also an interaction with plant and animal uptake and storage.”
Typically, when most people talk of nutrition, the focus is on macronutrients: fat, carbohydrates and protein. The fat and carbohydrates are our major energy sources, whereas the proteins are the building blocks for our cellular structure and metabolism.
But, micronutrients are also vital as cofactors for all the metabolic reactions in our body. We, therefore, need a minimum daily intake of vitamins, minerals and trace metals which are present in varying amounts in our food. Typically, the richest source of these three micronutrient groups are plant-based foods i.e. Fruit and vegetables. The suggested minimum daily intake of fruit and vegetables is 2 to 3 pieces of fruit per day and 3 to 5 servings of vegetables per day (one serving of vegetables, as an example, is half a carrot). It is a concerning fact that less than 10% of the population of Australia would consume this minimum recommended amount of fruit and vegetables on a daily basis.
I have attached a table from Harvard University suggesting the recommended daily intake of vitamins, minerals and the common trace elements. There are, no doubt, variables relating to age, sex and physical activity but for the majority of adults, these differences are small. Thus, the recommended daily intake for adults is sufficient.
There is no doubt that there is a strong variability in the quality of soil around the world. For example, in rural China there are soil deficiencies in selenium & iodine, two common minerals. There is significant conjecture in the medical field as to the significance of selenium deficiency but there is a strong relationship between this deficiency and a cardiomyopathy seen in cows. There is also no doubt that iodine deficiency has led to cretinism and other significant thyroid disorders in parts of the Chinese population.
Although Australian soil is not as deficient as the soil in other parts of the world, there is still concern that the quality of our fruit and vegetables has deteriorated over the past 50 years for a variety of reasons, some of which have been mentioned by the author of the question above.
The interesting question here is whether taking vitamin supplements adds any benefit to health? Most doctors will tell you that all vitamin supplements do is give you expensive urine. But, if you take a more global view of the wider medical literature, in many instances, supplements also give you expensive blood, which is exactly what you want.
Over the past 30 years, Harvard University has been performing the Male Physicians trial and the Nurses Health study. They have examined the health behaviour and parameters of 180,000 people over this time. To take the example of multivitamins, up to 10 years in the male doctors, there was no benefit from taking a daily multivitamin. But, when the 10 year data was analysed, there was an 8% reduction in common cancers and cataracts in those doctors randomised to a daily multivitamin. When the 15 year data was analysed in the Nurses Health study, there was a 75% reduction in bowel cancer, a 25% reduction in breast cancer and a 23% reduction in cardiovascular disease, just by taking a multivitamin on a daily basis. When the 20 year data was analysed in the males, there was a 44% reduction in cardiovascular disease in those doctors who persisted in taking a multivitamin daily over this period.
Thus, the vital importance of having a significant dose of vitamins, minerals and trace metals on a regular basis. In my view, fruit and vegetables are still the best source of these vital nutrients but you do gain added benefit from the daily ingestion of high quality supplements.