Its the biggest killer in the first world, causing heart disease, and being more addictive than cocaine.
A massive(no pun intended) portion(again, no pun intended) of America is obese.
Sugar isn't only linked to that health problem, its linked to basically all chronic diseases indirectly,
cancer https://www.bulletproofexec.com/low-carb-paleo-diets-vs-cancer-a-follow-up-note-to-steve-jobs/ , http://www.ncbi.nlm.nih.gov/pubmedhealth/behindtheheadlines/news/2016-03-08-carbs-linked-to-lung-cancer-study-finds-/
Now you might be wondering why it does so much bad at once. I researched it before, what I saw was basically some sugars when broken down cause acidity in our blood stream. The bones lose calcium to create something to help balance the ph levels in your blood, calcium loss is one problem related to arthritis. Now acidic blood causes increased vein damage causing problems to the lungs eyes brain and heart which use the veins most. Severe diabetics do have an increased risk of Alzheimer's, going blind, losing their legs due to vein circulation problems, but that could be attributed to lack of exercise right?
Yeah, all these problems also usually exercise helps with, but not always. http://breakingmuscle.com/nutrition/an-athletes-guide-to-inflammation-what-to-eat-and-what-to-avoid Athletes get inflammation too.
A little food for thought, also side note, those with more health problems contribute more to family stress which can contribute more to mental illness, stress being a factor(meaning it could cause all sorts of economic and social problems secondarily). For instance http://www.medicaldaily.com/pasta-and-depression-grains-and-other-carbs-could-be-affecting-your-mood-261266 and that's before counting social factors. Having a house full of moody people isn't going to be grand. Also did other related research not much worth mentioning aside from some vitamins can help prevent both hangovers, and sugar damage (because antioxidants prevent inflammation etc yada yada)
Also worth noting not all sugars are equal, http://www.greathealth247.com/ph-acid-alkaline-food-chart.html I had a different chart before but this should do. Studies say though for the brain some carbs are useful but moderation matters, And what kind matters, not just one or the other, moderate the good kind, have none of the bad is the challenge.
So you wanna be nicer to friends n family, can't help but be moody? Try a diet change and work in some exercise if you aren't already.
Sugar, number one first world problem.