Vitamin B9 is known as folate or its synthetic form folic acid and is one of the 8 B vitamins which makes up the B complex family. Vitamin B9 is water-soluble which means your body does not store it and can be rapidly depleted.
One of the main functions of all the B vitamins is converting carbohydrates into glucose which helps the body produce energy. B-complex vitamins are needed for healthy skin, hair, eyes, and liver. Many of the B-complex vitamins also play an important role in keeping the nervous system healthy and the brain functioning properly.
Folate is derived from the Latin word ‘folium’ which means ‘leaves’ in reference to being first found in spinach.
Needed for energy production, blood formation and protein synthesis
Vitamin B9 (Folate) is needed for forming red and white blood cells and helps the body to use amino acids and energy production. It is critical for many functions with the body and works alongside many of the B vitamins and essential minerals. The following are some of the health benefits linked to adequate intake of folate.
Prevents mood disorders
Vitamin B9 can regulate a healthy mood and overall wellbeing. This can have a positive impact and help with sleep. Deficiency of folate can lead to insomnia, irritability and depression.
Some studies are showing positive results with folate in mood related disorders such as depression. 
Supports brain health and neurological functions
Some studies have found a link between folate deficiency and neurological conditions such as epilepsy, cognitive decline, Parkinson’s, Alzheimer’s and dementia. Some parts of the brain needed for cognitive functions such as memory and learning are affected by folate deficiency. Additionally high homocysteine levels have been associated with neurological disorders which can also be an indicator for low levels of folate and other deficiencies such as B6 and B12.
Deficiency of folate can cause oxidative damage to brain cells leading to cognitive decline. In addition to B9 vitamin B12 is also needed to help the nerves function properly.
Promotes a healthy pregnancy and prevents birth defects
A deficiency of folic acid in pregnant women can lead to neural tube defects. In some countries foods fortified with folic acid is mandatory in order to reduce the risk of neural tube defects in babies. During pregnancy folate requirements increase in order to help with fetal development.
Improves fertility in men
Some studies are showing a link between the health of sperm and folate levels. Low folate levels have shown to have an impairment in the sperm structure. Other studies have shown fertility improvement in men correcting nutritional deficiency with folate supplement with improved chance of pregnancy most likely due to improved sperm health.   
Folate is required for the formation of red blood cells (oxygen-carries) which when deficient can lead to megaloblastic anemia. In cases of anemia caused by a folate deficiency supplementation can usually reduce feelings of tiredness and fatigue however it is also important to check for other deficiencies such as iron, B12 and copper which are all associated with anemia when levels are low.
Supports heart health and improves homocysteine levels
High homocysteine levels damage blood vessels and have been linked to cardiovascular disease, thrombin generation and neurodegeneration. Studies are showing vitamin B9 in addition to vitamin B6 and B12 can help lower homocysteine levels which helps to protect blood vessels and reduce the risk of cardiovascular disease and other health conditions linked to high homocysteine levels. Folic acid can also control or contribute to normal levels of cholesterol by reducing LDL cholesterol level. Maintaining cholesterol levels is important for heart health.    
High levels of homocysteine can also lead to strokes and keeping homocysteine levels normal can prevent the condition. Some studies have shown that folic acid supplementation can be effective in preventing stroke in those with cardiovascular disease. 
Reduces the risk of colon cancer
Studies are showing a link between colon cancer and folate intake which suggests a deficiency could lead to colon cancer. Intake of dietary folate has been associated with a reduced risk for colon cancer. However these studies are mostly referring to the natural form folate whereas synthetic form folic acid can actually increase the risk of cancer which may be due to excessive intake as folic acid is more difficult to eliminate. 
Prevents age-related macular degeneration
Various factors influence the risk of developing age-related macular degeneration and includes a deficiency of folate. One study has shown that a deficiency of folate and B12 increases risk of age-related macular degeneration with a number of participants supplementing with in these vitamins showing a reduced risk. 
Vitamins: B2, B3, B5, B6, B12, C
Minerals: Cu, Fe, Mg, Zn
Other: Folate binding proteins (FBP)
Vitamin B9 (Folate) works synergistically with vitamin B12 and vitamin C to help the body synthesise and process protein.
Vitamin B9 needs B12 for the methylation cycle. 
Metals: Al, As
Other: medications (metformin, methotrexate, triamterene, trimethoprim, phenobarbital, phenytoin, sulfasalazine), congenital or acquired enzyme deficiency, folate conjugase inhibitors (legumes (lentils), cabbage, oranges), alcohol, UV exposure  
Foods that contain significant amount of folate include liver, legumes (lentils, beans, peas), whole grains (brown rice), poultry, pork, lamb, cheese, eggs, shellfish, leafy green vegetables (spinach, turnip greens, asparagus, kale), broccoli, cabbage, brussels sprouts, beetroot, brewer's yeast and oranges. Vegetables containing folate are better eaten raw or lightly steamed as heat destroys folate or folic acid. Folic acid can be found in many fortified foods such as cereals and bread which can be found on the food label.
The amounts recommended for vitamins and minerals are different for each country which can be found on the government website of host country. The nutritional data for each country are based on scientific research which are presented by the scientific academies in each country to help advise governmental departments for food and human nutrition.
Below is a list of some of the countries and the EU for which nutritional guidelines are available found on corresponding official government website (including the national academy of science website for the USA).
Australia and New Zealand
Vitamin B9 is available as folate which is also naturally occurring in food and as folic acid which is the synthetic form. It is available as capsules, tablets, liquid and multivitamin formulas such as vitamin B complex. Although folic acid has been shown to be better absorbed folate from the diet is considered to be highly bioavailable. Most people who eat high carb diets such as breakfast cereals, bread and other fortified foods may already be getting sufficient amounts. Pregnant women require more folate and may need more folic acid supplements to prevent birth defects. 
The natural form of folate is listed as L-methylfolate on supplement ingredients label. This form is the active form of folate and better utilized by those with a mutation of the gene and enzyme Methylenetetrahydrofolate reductase (MTHFR). Folic acid is converted into the active form of folate through the MTHFR gene however this function may be affected in some people which will impair the conversion folic acid to its active form. Unlike folic acid the active form L-Methylfolate is also able to cross the blood-brain barrier. This is essential for the synthesis of the neurotransmitters (serotonin, dopamine and norepinephrine) which can help with mood regulation.
The following are deficiency symptoms of folate:
- Fatigue / Tiredness
- Low energy (lethargy)
- Sore tongue (Glossitis)
- Loss of appetite
- Weight loss
- Heart palpitations
- Shortness of breath
- Mental / behavioral disorders
- Difficulty concentrating
- Memory problems (Forgetfulness)
- Anemia (hemolytic, megaloblastic)
- Shortness of breath (breathlessness)
- Feeling faint
- Pale skin
- Abnormal fetal development (neural tube defect)
- High homocysteine levels
- Vascular degeneration
- Cervical dysplasia
- High blood pressure
Vitamin B9 deficiency can increase the risk of heart diseases and the development of some cancers. Risk of vitamin B9 deficiency is high amongst pregnant and breast feeding women due to fetal growth and the loss of folate through breast milk.
The following are some of the causes of folate deficiency:
- Inadequate intake
- Breast feeding (Lactation)
- Excessive alcohol intake
- Malabsorption (Celiac disease, Crohn’s disease )
Sufficient daily intake of folate is required since folate is a water soluble vitamin it will not be stored in the body and may get depleted.
Heat and prolonged cooking destroys folate.
In a folate deficiency associated symptoms such as anemia, or high levels of homocysteine, methlymalonic acid (MMA) is normal whereas in a B12 deficiency MMA levels rise. This is an important factor which can determine whether B9 or B12 deficiency is associated with anemia and high homocysteine levels.
Folic acid can be toxic in chronic high doses through supplements. The following are symptoms of folic acid toxicity:
- Abdominal bloating
- Excess gas production
- Stomach upset (abdominal cramps)
- Skin reactions disorders (rash)
- Sleep disorders
- Behavioral changes
- Kidney damage
- Loss of appetite
- Increased cholesterol LDL / HDL ratio
- Zinc deficiency (increasing requirement)
- Potassium deficiency (increasing requirement)
- Asthma / respiratory tract infections
There are some studies that have shown that taking folic acid alone for treating pernicious anemia may mask a B12 deficiency however the therapies used currently for folic acid usually now uses B12 in addition to folic acid. 
There is an increased risk of cancer with high folic acid and vitamin B12 supplementation. There is also increased risk of oral cleft malformations from high folic acid intake.
Toxicity is more likely from folic acid supplements as it is not as easily eliminated from the body unlike the natural form folate.
People taking zinc or estrogen should avoid taking with folic acid as it may interfere with absorption.
When taking any medications it is important to discuss with your doctor or other health professional before supplementing with any form of vitamin B9 supplements as it may interact or inhibit the effects of various drugs.