As MSM dietary advice goes, this is actually pretty well done and useful. One point they under-emphasize (most nutrition articles miss this) is that for vitamin D production, it is really useful to get outside even if it is only for 15 minutes of time in the sun. We over-estimate the risk of skin cancer and under-estimate the risk of too little vitamin D. It’s not just gaming that keeps people indoors, it’s the constant hand wringing about skin cancer. If you want to understand the risk factors for skin cancer read this.
Not only does sunshine promote vitamin D production all throughout life (although less in the 8th decade and beyond), it boosts serotonin, which plays a critical role in mood.