The majority of people take months, even years to properly understand how methylation works and why a functioning methylation cycle is crucial to good health.
A formal explanation of methylation describes it as… “Reactions in our metabolism that involve the transfer of a methyl group (a carbon with three hydrogen’s attached) from one compound to another.
These reactions are required for many of the most vital pathways in our metabolism.
The building or repair of every cell in our bodies requires methylation.” (Cynthia Schneider, MD).
This definition is great but unless you have a science background it will not help you to comprehend the importance of methylation and why it is so essential.
Methylation and our bodies
Methylation allows the body to take action against stressors in our environment, helping it to detoxify, adjust and rebuild.
It is involved in many of our most vital bodily functions, by offering support and/or managing, such processes as:
- Controlling inflammation
- Maintaining DNA
- Immune function
- Energy production
- Mood balancing. 
Dr Amy Yasko (Ph.D., NHD, AMD, HHP, FAAIM) owns an integrative healthcare practice in America which specialises in chronic inflammation, immunological and neurological disorders, (including Autism and other spectrum disorders).
Dr Yasko has extensive expertise in biochemistry, molecular biology and biotechnology, and correcting damaged methylation pathways usually plays a prominent role in her treatment protocol.
She feels a significant portion of chronic conditions seen today are the result of a dysfunction in methylation pathways.
Dr Yasko writes how “methylation is involved in almost every bodily biochemical reaction, and occurs billions of times every second in our cells… (which is) why figuring out where the cycle can better perform its tasks contributes to health improvement, and reduced symptoms.”
Some of the conditions she says are linked to poor methylation include; cardiovascular disease, cancer, diabetes, adult neurological conditions, autism and other spectrum disorders, chronic fatigue syndrome, Alzheimer’s disease, miscarriages, fertility, and problems in pregnancy, allergies, immune system, and digestive problems, mood and psychiatric disorders as well as the aging process. 
The two most effective biomarkers for methylation are whole blood histamine (an important protein involved in many allergic reactions), and absolute basophils (a type of white blood cell).
However, it is important to note that although whole blood histamine is a marker for an inherent methylation tendency, it does not indicate the wellness of a patient.
These biomarkers help distinguish patients between having tendencies of “under” or “over” methylation. 
Methylation is a major factor in the production of serotonin, dopamine, and norepinephrine in the body, and this is why undermethylation can lead to a depletion of these three essential neurotransmitters.
Undermethylation can also result in some of the following characteristics – phobias, delusional behaviour, obsessive compulsive disorder (OCD), frequent headaches, denial of illness and non compliance, difficultly with transitions, seasonal allergies, high achiever, a strong will, highly motivated, addictive behaviour, calm demeanour with high inner tension, social isolation and sparse hair growth. 
The common biochemistry of UNDERMETHYLATION is:
- High blood histamine
- High basophil count
- Low plasma zinc
- Elevated serum copper
- Low homocysteine
- High heavy metals
- Low levels of the neurotransmitters serotonin, dopamine and norrpinephrine. 
Overmethylation can cause some of the following characteristics – high anxiety/panic, poor achiever and low motivation, artistic/musical ability, low libido and overweight, easily frustrated, sleep disorder and paranoia, depression and self isolation, self mutilation and nervousness, tinnitus (ringing in the ears), food/chemical sensitivities, high pain threshold, past history of ADHD, hyperactive psychosis, grandiosity, nil family history, hirsutism and eczema/dry skin. 
The common biochemistry of an OVERMETHYLATION is:
- Low blood histamine
- Low basophil count
- Low plasma zinc
- Elevated copper
- Elevated levels of the neurotransmitters serotonin, dopamine and norepinephrine. 
- Dr Amy. www.dramyyasko.com (updated: 2013, visited: July 2013)
- Dr Richard H Stuckey. Targeted nutritional treatment of metal illness. www.biobalance.org.au/_downloads/targeted-nutritional-treatment-of-mental-illness.pdf (visited July 2013)