Where do we come from?

The human body is a rather complex operation.  Multiple organ systems lumbering around in a mobile casing which is home to billions of different organisms.  This intricate being is constructed using combinations of chemical elements, the building blocks of our universe.  Eleven different chemical elements make up 99.9% of the mass of a human.    So what is the source for these elements that we must absorb in order to become who we are?  For a great many of these elements it is the soil.

While volunteering for a soils education exhibit, I accosted an unfortunate visitor or two and asked them where the magnesium in their bodies came from.  Interrogating strangers on where they get their nutrients from can feel wierd. It seemed a poster with pictures would be a better way to illustrate the fact that magnesium in our bodies comes from the soil.  So then, to answer all your deep questions as to your origins:

The poster is also the work of one Jessi Barber who works for the education exhibit.  She was kind enough to replace all the photos I had just grabbed off the internet with photos her organization had taken.  She also fixed the text so it was a little more to the point.

Of the elements humans need to live, Oxygen, Carbon, and Hydrogen make up 96% of our bodies.  Nitrogen makes up another 3% which shows why it is such an important fertilizer.  Yet just because other elements represent a smaller fraction of our mass does not mean they our less important.  A human without any Phosphorus will be just as non-existent as a human without Carbon.  

We get 12 of the 18 core elements we need to survive from the soil via plants and animals we eat.  Carbon, the second most abundant elements in our bodies comes from plants and animals we eat, but the source of this carbon is from the air.  Plants photosynthesize carbon dioxide and water to form sugar and then more complex carbohydrates.  

Here are the primary sources of the 18 core elements that compose our body, in order of abundance by mass:

Oxygen - From water we drink and air we breathe

Carbon - From plants which take it out of the air as carbon dioxide

Hydrogen - From water we drink

Nitrogen - From plants which uptake it from SOIL

Calcium - From plants which uptake it from SOIL

Phosphorus - From plants which uptake it from SOIL

Sulfur - From plants which uptake it from SOIL

Potassium - From plants which uptake it from SOIL

Sodium - From salt

Chlorine - From salt

Magnesium - From plants which uptake it from SOIL

Iron - From plants which uptake it from SOIL

Zinc - From plants which uptake it from SOIL

Copper - From plants which uptake it from SOIL

Selenium - From plants which uptake it from SOIL

Manganese - From plants which uptake it from SOIL

Iodine - From iodized salt and sometimes from plants via soil

Molybdenum - From plants which uptake it from SOIL

Whenever plants are harvested, the elements they have absorbed into their tissues are removed from the soil on which they were grown.  These elements must be replaced in the form of fertilizers or compost otherwise the soil will become deficient in the these elements and plant growth will suffer.  Capturing these soil nutrients in our waste streams (like when we compost) is an important way to help maintain the soil fertility of our farmland.

Originally I had written, "The human body cannot survive without 16 key elements".  With this wording you're still in the right if somebody wants to tack on Bromine, Cobalt, Nickel and some other trace elements to this list.  The important thing is to not say, "The human body needs 16 elements to live, no more, no less." I've changed the poster a little to reflect 18 core elements as discussed in this blog post. If we include elements the body will use in extremely trace amounts, 36 elements have been found to play a positive role in human health. I'm sure that number will differ depending on what authority you ask and will fluctuate as new research comes out.

Even something pretty far off our radar such as Rubidium is important for the health of humans....or at least the health of "she goats": Recent progress in exploring the essentiality of the ultratrace element rubidium to the nutrition of animals and man.  Whether or not the body could survive without some of these elements and simply live in poorer health is another question.  If you want to know more about the elements required for human life check out Chapter 16. Ultratrace Minerals in Modern Nutrition in Health and Disease or the wikipedia page, Composition of the Human Body

The number of elements actually found in the human body is usually 42. For a detailed list see this table: Estimated Atomic Composition of the Lean 70-kg Male Human Body. (Somewhat worrisome for the credibility of this source is that they say there are normally 41 elements present and then list 42!)  

Thankfully, if we have access to whole foods grown on fertile soils, we rarely have to think about the amount of specific elements are bodies are recieving.