Page 190 - Berkshire Encyclopedia Of World History Vol Two

disease and nutrition 539

are to spread infections. It also reflects the interaction of iron stores are in fact so important in this regard that the
humans with the life cycles of reservoir species that store human body may make itself anemic by sequestering iron
the parasites and vectors that transmit them, and the lim- to deprive invading bacteria. However, some parasites
its imposed by microenvironments and broad climate or can actually synthesize the nutrients they need.
soil zones in which parasites, reservoirs, and vectors In addition, infections interact with other infections.
must live.As human behaviors change, parasite reservoirs One infection—AIDS, for instance—facilitates another
and vectors, particularly microorganisms, have shown a by suppressing the immune system or by preparing cells
remarkable ability to adjust or evolve new genetic pat- physically and chemically for invasion. However, an
terns to adapt to new circumstances. infection with some microorganisms, themselves rela-
Human nutrition depends on human interaction with tively benign, can help the body fight off other parasites.
the natural movement of forty to fifty nutrients (carbo- Malnutrition resulting from the lack of any one nutri-
hydrates, lipids, vitamins, amino acids, energy, minerals, ent can be affected by the lack or excess of other nutri-
water, and fiber) through soils and through other organ- ents. For instance, a low intake of vitamin C or protein
isms. It also depends on several other factors: the ability from animal sources limits the digestion and absorption
to obtain specific foods; the combination of foods eaten of iron, as does a high intake of phytates and oxalates
and eaten together; the range of soils exploited; the ab- from vegetable sources. The body’s use of calcium
sence of nutrient antagonists and toxins; food prepara- depends on the availability of phosphorous.
tion and storage; digestion, absorption, retention, and
storage within the body; dissemination to, and utilization How Human Behavior
by, individual cells; and balanced elimination. And fi- Affects Disease
nally, human nutrition involves the avoidance of danger- Human behaviors that affect our interactions with nutri-
ous overingestion or absorption, since some vitamins and ents and diseases are partly a result of idiosyncratic
minerals (and, in the modern world, salt, fats, calories, behaviors of individuals or groups, and largely a function
and dietary carcinogens) can occur in excess. of a sequence of cultural changes in history and prehis-
tory.The changes obviously overlap one another in time,
How Nutrition but a rough sequence is as follows: population growth
Affects Disease and spread into new environments; increased population
Nutrition and infectious diseases interact significantly density; the shift from foraging for wild foods to farming
with one another. Infectious diseases tend to exacerbate or herding of domesticates; sedentism (living perma-
malnutrition by causing nausea, by consuming nutrients nently in one place); accelerating population growth;
within the human host, by causing diarrhea (the exces- increasing size of political units and individual centers of
sively rapid transit of food through the gut that reduces population (towns and cities); increasing size and speed
the chances for absorption), and by diverting needed of trade networks; the emergence of civilization (central-
nutrients to fight the infection. Malnutrition facilitates the ized governments reinforcing class stratification by force);
spread and significance of infection primarily by depress- the growth of industry; and the emergence of the modern
ing the host’s immune system and rendering tissues sus- world system.
ceptible to parasite attack. This combination can be These trends and their influence on health can be doc-
observed in the interaction of childhood malnutrition and umented partly through historical sources and archaeol-
infantile diarrhea. ogy and partly through the analysis of skeletons in pre-
In a few cases malnutrition may help prevent infectious historic and historic contexts. Trends in health can also
disease. Low iron stores in the body may limit the abil- be reconstructed theoretically using our knowledge of the
ity of iron-dependent bacteria to invade the body. Low chemistry of particular nutrients and the contemporary