The short answer is you need to know what you are putting into your body. Once fully grown most adults benefit from calorific restriction or simply putting less food in your mouth which has been proven to increase longevity.
Comparing supplements helps you understand the ingredients of each tablet and how they may affect your health.
In Australia, the Therapeutic Goods Administration (TGA) regulates all medicines including prescription, over-the-counter and complementary medicines. The TGA ensures that Australians have access to “quality therapeutic goods that are safe to use and fulfil their intended purpose”. The TGA refers to health supplements as traditional or alternative medicines.
In New Zealand Medsafe is the regulatory body for health supplements. In the USA the regulatory body is the FDA.
Pharmaceutical drugs are regulated and tested before being used by the public. Registered medicines must display the R number on the packaging. https://www.tga.gov.au/registered-medicines.
In Australia some complementary medicines are evaluated and registered. All registered alternative medicines have a code eg Elevit is 213113.
If the ingredients of the complementary medicine is deemed low risk and is in acceptable amounts the supplement is not tested but is listed on the Australian Register of Therapeutic Goods (ARTG) .