Several harmful effects of nitrogen on human health include causing vitamin A shortages, decreasing function of the thyroid gland and decreasing the blood's ability to carry oxygen. These effects are seen when nitrogen occurs in an ion form, such as nitrite or nitrate.
Decreased thyroid function and vitamin A shortages are both caused by nitrate. Nitrite reacts with hemoglobin in the blood, causing it to not carry oxygen as well. Both nitrates and nitrates cause the formation of nitroamines, which are known carcinogens.
While there are negative consequences of nitrogen, it is an important molecule within the human body that functions in the cardiovascular, immune, and central and peripheral nervous systems.