If I was to pick one supplement everyone needs to be taking is B Complex because you bodies chemistry pathways require the B's at almost every step to make energy.
Vitamin B1 (thiamine) aims to ensure that the body can produce new, healthy cells. It has also been reported to possess anti-stress properties, in addition to the ability to boost your immune system. Vitamin B1 is also essential for the breakdown of simple carbohydrates.
Vitamin B2 (riboflavin) helps to get rid of particles in the body which can damage our cells. B2 has also been linked with the potential prevention of early ageing, in addition to the ability to reduce your risk of heart disease .
Furthermore, B2 is essential for the production of red blood cells and haemoglobin, which is responsible for ensuring that the rest of your body’s cells receive the oxygen that they require. There have also been studies  which suggest that vitamin B2 can help in overcoming migraines, however, the results are not conclusive.
One of the main uses of vitamin B3 (niacin) is to increase the levels of high-density lipoproteins (HDL) in the blood. These are the so-called ‘good cholesterol’. The higher your HDL levels are, the lower your overall cholesterol levels are. This means you are at a lower risk of developing cardiovascular diseases (CVD).
Pantothenic Acid (B5)
Vitamin B5 can be found in pretty much all foods, albeit in small quantities. Its main responsibilities include breaking down fats and carbohydrates for energy, and the producing of important hormones such as testosterone.
Vitamin B6 has several different qualities which are a little less known of. First of all, it works to regulate the levels of homocysteine (an amino acid associated with heart disease). Furthermore, it helps to body to produce hormones such as serotonin and melatonin, as well as norepinephrine. These are sleep and stress hormones so will alter your mood and energy levels.
Vitamin B7, also known as the beauty vitamin, has several benefits when it comes to your appearance. It has been linked with improving the appearance of skin, hair and nails.
Vitamin B9 has several key benefits. It has been linked  to the prevention of memory loss, as well as improving depression. It has also been linked with the growth of the babies, to prevent birth defects.
The main role of vitamin B12 is to aid the other B vitamins in completing their ‘jobs’. It works with folate to produce red blood cells as well as to produce haemoglobin.