Vitamins and minerals are organic and inorganic compounds, respectively. Both groups of compounds are vital to the health of humans. Plants can manufacture vitamins and so consuming a high plant diet provides a wide range of vitamins. Minerals are also present in plant foods but in contrast to the vitamins, the mineral content of plants is dependent on the soils upon which the plant is grown. This is because plants cannot manufacture inorganic elements, but must derive them from the soil through absorption to their roots. High mineral soils therefore provide plants with high mineral tissues, and when animals and humans eat the plants they absorb the minerals to their own tissues. This is how many of the essential minerals in the human diet are obtained. Low quality agricultural soils therefore produce crops devoid of minerals and this produces mineral deficiencies in the people that eat these crops. High mineral soils have been prized by societies and are linked to the rise of empires because of the health populations they produce.
Certain agricultural soils are known to contain low levels of particular minerals and this produces populations of people who have mineral deficiencies. New Zealand for example is known to possess selenium poor soil and this causes poor selenium status in the New Zealand people who rely on crops grown in these soils. For example, the blood selenium levels of residents of Hamilton in the North Island are known to be historically low. The blood selenium levels of Hamilton residents were measured between 1973 to 1980 and found to be between 57 and 87 ng/mL1. These estimates were suggested to be accurate based on the part New Zealand wheat and part Australian wheat eaten by the residents (which had 11 and 150 ng per gram selenium, respectively). Improvements in the selenium status of the Hamilton residents were observed during 1970’s with the importation of this Australian wheat. The high selenium flour made from imported wheat is likely the reason that the selenium status of the North Islanders improved.
It is possible that the rise in selenium concentrations in the North island could have occurred through increased consumption of fish. However, for the increase to have occurred fish consumption would have had to treble in this period, and this was not the case. In addition, selenium salts added to livestock feed can supply additional selenium, but selenium salts added to livestock feeds did not coincide with improvements in selenium concentrations in Hamilton residents. However, in Dunedin and Tapanui the blood selenium did not change when Australian wheat was imported to New Zealand in 1971, 1976 and 1980. This likely reflects the fact that the South Island did not use large amounts of imported Australian wheat, but instead relied on wheat grown in New Zealand soils. The South Island is responsible for over 90 % of the wheat production in New Zealand and the mean blood values of the residents of Dunedin and Tapanui reflect the soil concentrations of the South Island closely.
Dr Robert Barrington’s Nutritional Recommendation: Obtaining adequate concentrations of trace minerals from foods is like playing russian roulette with your health. High quality foods should contain adequate trace minerals, and therefore food should provide adequate nutrition to humans. However, the trace mineral content of plant foods is dependent on soils quality. And as has been shown on many occasions, some agricultural soils are devoid of particular trace minerals. Taking a trace minerals as supplements is not ideal, as it is far better to obtain trace minerals from food. However, as an insurance policy against mineral deficiencies caused by low mineral crops, supplementation is an important consideration. Selenium is also present in foods of animal origin, and in many cases these sources can make considerable contributions to intake. Fish is also a good source of selenium, but concerns over pollution of selenium containing fish call into question the wisdom of high intakes of non-organic fish.
RdB
