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:
"To further the use of harmonized sanitary and phytosanitary measures between Members on the basis of international standards, guidelines and recommendations developed by the relevant international organizations, including the Codex Alimentarius Commission."
In fact, Article 3.1 of the Agreement goes even further than this to state:
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.
This is where possible future legal battles may arise on the international trade level in order to sort out "voluntary" from "mandatory" legal interpretation. On one side the natural health industries, practitioners and consumers and on the other side Codex, the WTO and our own government who's main interests may or may not be influenced more by international relations and trade pressure.
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.