However, the preamble to the SPS Agreement (to which all WTO Members are signatories) specifically mentions Codex and states that WTO Members (and hence all SPS signatories) desire:
In fact, Article 3.1 of the Agreement goes even further than this to state:
"To harmonize sanitary and phytosanitary measures on as wide a basis as possible, Members shall base their sanitary or phytosanitary measures on international standards, guidelines or recommendations, where they exist."
The key word here, from a legal point of view, would appear to be the word, "shall," which could perhaps be said to make the Guidelines for Vitamin and Mineral Food Supplements mandatory for all WTO member countries.
What about Countries that choose to continue to ignore Codex?
Even if a country decided not to follow Codex guidelines and standards, the standards that the refraining country does employ in place of Codex standards remains subject to a wide range of conditions as set out in detail in Article 5 of the Sanitary and Phytosanitary Measures (SPS Agreement).
In relation to dietary supplements, one of the most important of these conditions would appear to be a requirement to take into account risk-assessment techniques developed by "the relevant international organizations."
And you should also note that guidelines on risk analysis are already under discussion at meetings of the Codex Committee on Nutrition and Foods for Special Dietary Uses. Unfortunately, the committee has already indicated that this work will be concentrating upon "the development of methodological aspects for over dosage of nutrients."
Other conditions that would blunt deviating "standards" utilized by non-conforming countries in place of Codex standards include;
A requirement to take into account economic factors as well as the relative cost-effectiveness of alternative approaches to limiting risks
A requirement to avoid arbitrary or unjustifiable distinctions in the levels of risk protection that it considers to be appropriate in different situations, if such distinctions result in discrimination or a disguised restriction on international trade
Again, the resultant impact of signing onto earlier trade agreements is that, even if a country decided not to follow a Codex standard within its own borders, they would remain subject to a wide range of conditions set out in detail in Article 5 of the Sanitary and Phytosanitary Measures (SPS Agreement) and thereby made to comply.