Sugar can suppress your immune system.
Sugar can damage the pancreas. (Which is the gland active in glucose and insulin responses.)
Sugar can cause hyperactivity, anxiety, inability to concentrate and crankiness in children.
Sugar can produce a significant rise in triglycerides.
Sugar can cause metabolic syndrome.
Sugar reduces high-density lipoproteins (HDL).
Sugar raises the level of neurotransmitters: dopamine, serotonin, and norepinephrine.
Sugar can cause hormonal imbalance – some hormones become underactive and others become overactive.
Sugar can make the skin wrinkle by changing the structure of collagen.
Sugar can cause tooth decay.
Sugar can lead to obesity
Sugar can cause heart disease.
Sugar can cause dyspepsia (indigestion).
Sugar can be intoxicating, similar to alcohol.
Sugar can aggravate premenstrual syndrome (PMS).
Sugar can worsen the symptoms of children with attention deficit disorder (ADD).
Sugar promotes excessive food intake in obese people.
Sugar plays a role in the cause and the continuation of acne.
Sugar can cause fatigue, moodiness, nervousness, and depression.
Sugar can ruin the sex life of both men and women by turning off the gene that controls the sex hormones.
For a 122 more reasons (and a bibliography, if you don´t just take my word for it. ;)): click here.