[Seeking clarification and offering feedback, rather than making assertions about a subject fairly far outside of my knowledge base]
Thanks for sharing this interesting piece; I can tell a lot of careful thought went into it!
A reader (like myself) who doesn’t really follow this literature is likely to wonder why Vitamin D is an important focus given the production of that vitamin through sunlight exposure. So from a rhetorical standpoint, the piece might benefit from a brief discussion of why this isn’t as good a mitigating technique as the reader may have assumed.
Pham et al. (2022) state that “[t]he sunlight exposure method could be insufficient for an ASRS in which UV is reduced, and dangerous in an ASRS in which UV is increased due to ozone layer destruction.”
A reduction seems plausible, but it seems that given baseline levels the production would have to be fairly sharply reduced in most places to pose a serious risk to many people (as they could compensate with longer exposure times and less clothing).
Of course, in colder climates further from the equator this would be less viable! This hints at a possible way to stratify your conclusions; it may be that we need to give significant weight to Vitamin D for food needed for those who live far from the equator especially in colder months (but not for people near it).
As far as increased UV scenarios, it might even not be possible to reduce many people’s UV exposure to below a level that would generate adequate Vitamin D. Those people will get their Vitamin D needs met. Moreover, unless the dangerousness scales more quickly than the Vitamin D creation rate, limiting outdoor time ~proportional to the increase in UV production would seem to mostly work. I have no idea how to model either of these, though.
So even after a skim of Pham et. al., I don’t feel like I understand whether Vitamin D is likely to be a significant and widespread problem after an ASRS or is a more theoretical (or at least speculative) risk.
Hello Jason, thank you very much for your comment and for taking the time to analyze the article in such detail.
The article was carried out in an exploratory and generalized way with the aim of determining which foods with vitamin D could be implemented in large-scale ASRS such as the one that could be generated by the injection of 150 Tg of soot into the atmosphere due to a nuclear war. However, the research focused on the comparison of these foods and not precisely on the discussion about the regions of the world that would be really affected by this phenomenon.
Vitamin D is produced naturally by the body when the skin is exposed to UVB radiation from the sun, which under normal circumstances would be a simple and efficient strategy to avoid deficiency. However, Pham et al. (2022) suggest that in a large-scale ASRS, where the amount of available solar radiation could decrease, this solution would not be sufficient. In particular, UVB radiation, which is key for the synthesis of vitamin D, could be especially affected due to the dispersion of aerosols in the atmosphere that could block part of the light that arrives naturally.
The risk would not be homogeneous throughout the world. As you point out, in regions close to the equator, where UVB radiation levels are naturally higher, people could compensate for the lack of light with greater exposure since the climatic conditions do not represent a negative effect on health. However, in areas further from the equator, such as colder regions with fewer hours of light, this solution would not be so viable. In these cases, depending on sun exposure for vitamin D synthesis would be insufficient, especially in winter, which would make it necessary to resort to fortified foods or vitamin D supplements as a prior strategy.
You also raise an interesting point about the scenario in which, instead of being reduced, ultraviolet radiation increases due to the destruction of the ozone layer. This would be a complex problem, although theoretically there could be enough UV radiation to produce vitamin D, prolonged exposure would be dangerous due to the risk of skin cancer and other problems arising from overexposure to radiation. In this scenario, vitamin D supplementation or food fortification would still be the safest option, as reducing sun exposure time would be essential. Vitamin D deficiency in an ASRS will likely vary by geography and the magnitude of atmospheric changes. While in some regions people could compensate with increased sun exposure, in others this would not be feasible, making food fortification and supplementation play a key role.
For this reason, I think that researching foods with vitamin D would not generate generalized solutions, but would propose solutions of high interest for regions that would be seriously affected by such a scenario.
I appreciate your comments again and I recognize that you mention aspects that would greatly enrich the study :).
[Seeking clarification and offering feedback, rather than making assertions about a subject fairly far outside of my knowledge base]
Thanks for sharing this interesting piece; I can tell a lot of careful thought went into it!
A reader (like myself) who doesn’t really follow this literature is likely to wonder why Vitamin D is an important focus given the production of that vitamin through sunlight exposure. So from a rhetorical standpoint, the piece might benefit from a brief discussion of why this isn’t as good a mitigating technique as the reader may have assumed.
Pham et al. (2022) state that “[t]he sunlight exposure method could be insufficient for an ASRS in which UV is reduced, and dangerous in an ASRS in which UV is increased due to ozone layer destruction.”
A reduction seems plausible, but it seems that given baseline levels the production would have to be fairly sharply reduced in most places to pose a serious risk to many people (as they could compensate with longer exposure times and less clothing).
Of course, in colder climates further from the equator this would be less viable! This hints at a possible way to stratify your conclusions; it may be that we need to give significant weight to Vitamin D for food needed for those who live far from the equator especially in colder months (but not for people near it).
As far as increased UV scenarios, it might even not be possible to reduce many people’s UV exposure to below a level that would generate adequate Vitamin D. Those people will get their Vitamin D needs met. Moreover, unless the dangerousness scales more quickly than the Vitamin D creation rate, limiting outdoor time ~proportional to the increase in UV production would seem to mostly work. I have no idea how to model either of these, though.
So even after a skim of Pham et. al., I don’t feel like I understand whether Vitamin D is likely to be a significant and widespread problem after an ASRS or is a more theoretical (or at least speculative) risk.
Hello Jason, thank you very much for your comment and for taking the time to analyze the article in such detail.
The article was carried out in an exploratory and generalized way with the aim of determining which foods with vitamin D could be implemented in large-scale ASRS such as the one that could be generated by the injection of 150 Tg of soot into the atmosphere due to a nuclear war. However, the research focused on the comparison of these foods and not precisely on the discussion about the regions of the world that would be really affected by this phenomenon.
Vitamin D is produced naturally by the body when the skin is exposed to UVB radiation from the sun, which under normal circumstances would be a simple and efficient strategy to avoid deficiency. However, Pham et al. (2022) suggest that in a large-scale ASRS, where the amount of available solar radiation could decrease, this solution would not be sufficient. In particular, UVB radiation, which is key for the synthesis of vitamin D, could be especially affected due to the dispersion of aerosols in the atmosphere that could block part of the light that arrives naturally.
The risk would not be homogeneous throughout the world. As you point out, in regions close to the equator, where UVB radiation levels are naturally higher, people could compensate for the lack of light with greater exposure since the climatic conditions do not represent a negative effect on health. However, in areas further from the equator, such as colder regions with fewer hours of light, this solution would not be so viable. In these cases, depending on sun exposure for vitamin D synthesis would be insufficient, especially in winter, which would make it necessary to resort to fortified foods or vitamin D supplements as a prior strategy.
You also raise an interesting point about the scenario in which, instead of being reduced, ultraviolet radiation increases due to the destruction of the ozone layer. This would be a complex problem, although theoretically there could be enough UV radiation to produce vitamin D, prolonged exposure would be dangerous due to the risk of skin cancer and other problems arising from overexposure to radiation. In this scenario, vitamin D supplementation or food fortification would still be the safest option, as reducing sun exposure time would be essential.
Vitamin D deficiency in an ASRS will likely vary by geography and the magnitude of atmospheric changes. While in some regions people could compensate with increased sun exposure, in others this would not be feasible, making food fortification and supplementation play a key role.
For this reason, I think that researching foods with vitamin D would not generate generalized solutions, but would propose solutions of high interest for regions that would be seriously affected by such a scenario.
I appreciate your comments again and I recognize that you mention aspects that would greatly enrich the study :).